obstruct, or hamper the passage of the m skrrks stena. please confirm you are not intending to unlawfully attempt to board the mv stena. >> no challenge is intended. no challenge is intended. i want to inspect the ship for security reasons, over. >> reporter: but the british suspect the real reasons is this. a tanker carrying iranian oil off the coast of gibraltar earlier this month. they suspected it was heading to syria in violation of eu sanctions. for weeks a furious iran has vowed a response. now they seem to have retaliated. authorities have promised a robust response to the seizure of the tanker. that means is being discussed by