officials as to the urgency, the imminence of an attack. the daylight is disappearing. it includes increased patrols, particularly around critical infrastructure, power plants, bridges. the reason is it is the u.s. intelligence view of this that those will be targets in a russian invasion of ukraine. >> and according to a senior ukrainian official, u.s. officials warned ukraine that they're particularly worried about a possible attack on the city of kharkiv outside the donbas region which putin has declared to be two independent states. going to kharkiv, that would be even more of an escalation. >> reporter: absolutely. it would be outside these fake, independent republics that have now been recognized by putin. so even further outside land called disputed. inside the sovereign borders.