0 casualties are unclear at this time. we will provide additional details when we can. we also learned moments ago that president biden has been briefed on that explosion outside of kabul airport. a white house official tells cnn. and we are waiting on a pentagon press briefing which will happen in about 30 minutes from now. the back ground on this, as you look at a live picture from the kabul airport, that in recent days and yesterday we reported the u.s. has been very concerned about a credible threat stream about potential terror attacks targeting the gates to the airport and the crowds around those gates. the u.s. believing that terror groups had both the capability and the planning to carry out such attacks. there is still no attribution for these attacks or as we said, any confirmation about casualties. we have our reporters covering the story. let's begin with nick paton walsh in doha. we see now a confirmed attack. >> -- only the families of the u.s. serve men concerned about who may have been on the airport at the time and also for the many afghans waiting outside. we don't know the reason behind this at this stage. it is an explosion. we haven't clarified precisely there are many things moving in that area. could be crowded areas so other reasons why there could have been a blast but it will play directly into fears of a possible attack. let me just tell you a little bit about where we think this might have occurred. in the out skirts of hamid karzai airport. no precise location. but there are many afghans waiting at key gates. there is one called abby gate and northeast gate and northern gates as well. people crowd to them. they're often huge metal doors essentially, i've heard people banging on them. it is an extraordinary noise of desperation and that is where we've seen the stand-off between afghan and u.s. marines and the crowds down below. the traffic is often blocked around there and i've seen video and heard reports that the taliban have been involved in using their presence as a sort of crowd filtration, vetting who is allowed to approach the gates and even more involve further away from the airport, further down the airport road. so it is unclear where this blast has occurred. it is certainly i think the worst news for anybody observing the situation closely. but it is sadly will most likely have fed into an area that is quite heavily populated. we've seen images of thousands, it seems, of afghans despite the news the gates are fully closed. there is at this point no way on unless you are essentially escorted or entry on to the airport is arranged by prior coordination by the taliban and the united states and even people who have half of that circulating around the base in buses this morning. people have still gone to the gates in large numbers. they've stood, i've seen videos of them standing in sewage water in the ducts along there below razor wire dangerous in the crush holding up pieces of paper demanding to be allowed in, making they're case as to why the nato allies should bring them on to the base. now obviously for those who have a distaste for the u.s. presence, they prove a target but coming out of the base there have been u.s. service members in the past, unclear what has occurred here but it is a sensitive and delicate target. so densely populated. >> no question, nick paton walsh. so let's remember what we have learned at this point. explosion outside of kabul airport. at one of the gates there. where there have been a number of crowds trying, clamoring to get in on to get on a evacuation flight out. our latest information it appears to be a suicide attack. that could be consistent with the kind of attacks that u.s. officials have been concerned about in the hours and days leading up to this. as we reported yesterday, a credible threat intelligence stream that the u.s. had about plots, planning and capability to carry out an attack targeting exactly a gate like this and exactly a crowd like this that has been gathering at these gates. i want to go now to sam kiley. he was on the ground until just yesterday morning among the journalists taking out of the country in part because of safety concerns. sam, this was the concern and the sad fact is the pentagon now confirming such an attack. >> reporter: yeah, the situation on kabul international airport for several days until i left yesterday evening, in fact, jim, was extremely tense. because they did have this very active ongoing intelligence with some precision. this he were anticipating a spectacular attack. they were anticipating an attack almost certainly against the crowds gathering outside of the gate. and they anticipated that it would be so-called isis-k, isis group behind it. we don't know yet officially in any great detail the providence of this bomb but all of the fingers will be pointing toward isis-k and the only organization jim in the world that has an interest in committing this kind of atrocity. because it does three things. it intimidates the afghan population, which is very much an isis tactic or even strategy. it embarrasses the taliban who had got a security deal, they were effectively running security in their own way and filtering out afghans, counter to american policy. but they were working with the united states. and then you have the united states running security for that multi-national coalition effort to get as many people out before they have to start withdrawing the themselves. this is a very vulnerable time. and the locations as nick said, he laid it out accurately, there are these bottlenecks that present themselves as fantastic targets for those cynical and violent terrorist organizations, probably the world has ever seen. they want the publicity and the attention. they want to humiliate both the taliban and the united states. and that is what they're trying to achieve with the atrocity of this nature. and on top of that they will make it harder for the last refugees to get out. >> sam kiley, as sam was speaking there, you could see that and i again i want to remind you this is a live picture from the kabul airport. what we saw crossing the screen was a chinnock double rotor helicopter, that is the clouds of smoke rising that the rotors brought up. hard to read in to what that is but that is activity at the airport and we'll bring you details more as we hear more about casualties, if they were casualties, who among those casualties, the pentagon confirmed an attack at gates and it is our latest information that this appears to be a suicide attack. that could be consistent with the tactics used by a number of terror groups who should be clear in afghanistan, though i should note that the particular concern leading up to this moment, this specific intelligence stream that we reported yesterday, focused on the group isis-k or islamic state corizan. many groups making a base home in afghanistan. let's go back to kylie atwood. kylie, i know you've been working your sources on this. are you learning any more details about the exact location of this attack or the possibility of casualties? >> reporter: yeah, jim, what ware learning is that this attack happened at one of those entry gates. that you guys have been discussing. these entry gates have been swarmed by afghans over the last few days, over the last ten days frankly trying to get into the airport. that would explain why we are hearing there are afghan casualties as a result of this explosion. now, we are told that this explosion looks like a suicide attack. that it was something that one person potentially going in, but we're looking to learn more about that. but significantly these gates have been closed largely for the last few days. as the united states has prioritized getting in americans. but the afghans have still been in large crowds outside of these gates. that is made the situation at the airport as the u.s. government has been tracking this isis-k threat, incredibly dangerous. and we heard just this morning from the top u.s. diplomat on the the ground in afghanistan who wouldn't talk about the threat streams that the united states was picking up. but used the word imminent to describe the threats that they are seeing that are possible. of course, what we're seeing now is something that they were likely tracking generally speaking. so this is going to be an incredibly quick evolving situation. we're looking to learn more. were there any casualties, was anyone hurt on the u.s. side as of now, there are no u.s. casualties that we are told. but we'll also watch to see how this impacts the evacuation effort. the united states is still flying americans out of the country. they warned those americans to stay away from these gates, just yesterday because of the threat stream that they were seeing. but right now what we're learning is that this was at one of those entry gates into the airport and it is suspected to be a suicide attack. >> kylie atwood at the state department. and if you could put the map up on the screen. this is a live picture at the airport looking toward the flight line, the runway there. the main entrances to the airport for civilians are on the south side. the civilian side for entry to the airport and that appears to be at one of the entry points where this attack took place. as i mentioned, it is our latest information it appears to be a suicide attack. that consistent with the tactics of a number of terror groups operating in afghanistan. it is also consistent with a warning, an intelligence threat stream that we reported on yesterday about plots and planning and capabilities for such an attack in and around the airport that the u.s. became aware of. that particular warning focused on one group, isis-k. there are a lot of bad groups and bad guys running around that country right now with capables to do something like this. john harwood is at the white house where we learned a short time ago that the president has been briefed on the attack. beyond that, does the white house have a reaction to this and do they have any plans to respond? >> reporter: well, the question is going to be how serious the impact of this event has been. important to recognize that we still don't know the gravity of this attack, assuming it was a suicide attack. what the impact was and how many casualties there were on the afghan side or the american side if there were any and the scale of that impact would likely dictate whether or not the united states feels compelled to respond. but this is the nightmare scenario. this is the kind of nightmare scenario that the administration have been worried about as they get to the end of this evacuation process. that vulnerability would be heightened as you had desperate people trying to to get to the airport crowding around the gates and that is why they've tried to encourage people to leave the airport unless authorized to come in. but this is precisely what president biden has worried about. of course, over the last couple of weeks, we have had up to this moment no reported u.s. casualties. and we've had no mass casualty events involving afghans at the airport. has this changed that situation? that is a question that we simply can't answer now. the president may know the answer because he's been briefed and has got access to information that we don't. we're in a wait-and-see mode. and it is possible that the pentagon at that 10:30 briefing will be able to lay out more detail about the scale of the attack and we'll see if the white house has anything to note as well. >> i did see a c-17 taxiing on the runway. we'll continue to monitor and see if that is an indication that flights continue despite the threat. what we saw a few moments ago when was a chinook double rotor helicopter flying across the screen. barbara starr is at the pentagon. is there any new information about what happened here, specifically about casualties. >> reporter: i think what don said is the operative word at the moment. somebody may well know but here at the pentagon they are not publicly saying anything about the possible of casualties. and i think it is very important to sort of take a deep breathe here and remember that there are u.s. military families who know their loved ones are serving at airport who are watching every minute of this and they want to get word about what has happened and if any of their loved ones are in jeopardy. just like the afghans who are at the airport. they're families are going to want to know if their loved ones have been hurt, wounded or even killed in this attack. a lot of people, the world's eyes focused on this airport and a lot of family members on all sides wanting to know what is happened to their loved ones. it is going to be important to remember that the pentagon has very strict notification procedures when any kind of potential, and we don't know yet, mas casualty incident happens. so we want to be very cautious about all of this. we simply have not yet had word from the pentagon. if, if there are injuries to u.s. personnel, there is medical treatment capability on the the airfield. the u.s. military doesn't go anywhere without its medics. but it is always a question of whether they will have to airlift people out of there if, and it is a big if, if there are serious injuries. so this is something that we'll be watching very closely. we're getting some initial indications that the 10:30 news conference scheduled here at the pentagon obviously may float -- may be delayed until later in the morning as they continue to try to gather information. what we know is from kabul to tampa, florida, the military headquarters for middle east operations, to here in the pentagon, meetings are continuous, phone calls are continuous as they try and gather information about what happened. >> yeah. listen, in situations like the military has priorities. one, make the situation safe. two, treat any injuried and do notifications as well. these are things we'll have to wait for to get more details. but let's tell you the details we know now. explosion outside of kabul airport. one of the gates. the gates you've been seeing pictures of in recent days with throngs of people trying desperately to leave the country. sadly the concern had a been leading up to this that terror groups including isis-k would target such gates, such crowds with the exact attention -- intention of creating fear. that is the credible intelligence leading up to this moment. our latest here on cnn is that it appears to be a suicide attack as well. we'll bring you more information as we get new details. i want to go now to sam kiley who only 24 hours ago was along with other journalists vakevacud in the country because of concerns about risks just like this one. as you're watching this unfold here, tell us what your reaction is? >> reporter: i think, jim, it is got a sense of tragic inevitability because of the lay down there, the security lay down bheen means that yes the taliban are patrolling and people walking around with weapons as the british and american military withdraw, there are fewer and fewer people to be on security. they won't have reduced security on the airport perimeter but there are less and less people around to monitor this situation. and in any case, very little they could do about it. if somebody walks in with a backpack and manages to sneak through and detonate a suicide bomb, that is frankly something that was top of anybody's mind a week ago. when you get large crowds like this, isis-k would see that as a target of opportunity that is almost irresistible given their agenda and clearly very acive and sadly no capability to -- [ inaudible ] and now the issue is scale. they love scale, isis. they love to be able to cause carnage on the the most graphic level to humiliate and embarrass the two key enemies which are the taliban and the united states. the taliban have been fighting isis and killing them in large quantities whenever they rise up because they want to dominate the islamic space there and because they learned their lesson of having given safe haven to al qaeda and have been working very hard, perhaps so much on emass kul ating al qaeda, but they have been working hard to stamp out the ultra violent brand of isis started in syria and started acrass afghanistan and trying to get a big publicity stunt if it is isis-k. it is also a very easy area to do a large amount of damage. the blast walls mean if you're close to it, you could almost magnify and channel if you have blast walls on either side of routes which for example exist on the way to the abby gate. that is a canal and a road that have -- the road has blast walls on other side so you could direct the blast up and down the road. there is nothing going out to the side. you get ricochet effect. so very deliberate tarngeting here and clearly something was imminent and now it seems to have happened, jim. >> the sad facts on the ground. sam kiley, thanks very much. our kylie atwood is at the state department as we continue to monitor news from kabul that continues to be a live picture there, an explosion at one of the gates to kabul airport where crowds have been gathering to get on, hopefully try one of the evacuation flights, our latest information is this appears to be a suicide attack consistent with intelligence about a threat in recent days, a threat to the airport. we do not have any confirmation of casualties and who would be among the casualties. kylie atwood at the state department, what is latest you're hearing there. the state department just yesterday warned americans away from the kabul airport specifically because of terror threats to the airport. >> reporter: yeah, that is right. just this morning the top state department official in afghanistan warned of an imminent threat, right. we know that yesterday they told americans to stay away, to leave the gates at the airport if they were there trying to get into the airport. of course to get on to these evacuation flights. it is good news that the united states put out that alert for americans frankly because it means hopefully thatsy lot of the americans that were there left. but the reality on the ground is that we have seen a tremendous number of afghans surrounding these gates, where we are reporting that this explosion happened. so what that means is that even with a suicide attack like this is suspected to be, you could have a large number of casualties. now we don't know how many afghans have died in this explosion yet. that is something that we're still trying to learn and i think it is fair to say that all of the government officials here at the state department, at the pentagon, at the white house are all trying to gather that information because this is such a fast-moving case scenario. this happens just recently. but the bottom line also is what does this do for the evacuation efforts for the biden administration? we have heard the president say he wanted to speed up the evacuation efforts by august 31st to get out because of the isis-k threat streams that they were picking up on the ground, jim. >> kylie atwood at the state department. as kylie was speaking there, and again this is a live picture of the flight line at kabul airport, you could see a flight taking off. it appear be one of the c-17s that has been the work horses of the evacuation operation. that potentially hopeful sign that they're able to continue the flights despite this attack. remember, in these situations, they start with securing the situation, taking care of the injured, getting word out and then moving on to the mission at hand. joining me now is someone to discuss this with a great amount ever experience, lieutenant general h.r. mcmaster, and long history of commanding forces deployed as well. h.r., good to have you on this morning. thanks very much. >> hey, jim. good to be with you under these terrible circumstance