The US army said on Friday it is using an unarmed surveillance aircraft to view the situation in the Strait of Hormuz and is in touch with US vessels in the area to ensure their safety.
British foreign Secretary Jeremy Hunt spoke with US Secretary of State Mike Pompeo over the Islamic Republic seizing two oil tankers in the Gulf. While the UK claims Iran had taken over two tankers, Stena Impero and Mesdar, Tehran claims responsibility for only one, Stena Impero.
Iran's semi-official Tasnim news agency said the second vessel, the British-operated Mesdar, had not been seized. It said the ship had been allowed to continue its course after being given a warning over safety and environmental issues.
"These seizures are unacceptable. It is essential that freedom of navigation is maintained and that all ships can move safely and freely in the region," British foreign minister Jeremy Hunt said.
Hunt later said, in comments reported by Sky News, that there would be consequences if Iran did not return control of the ships but said Britain was not considering military options.
One fifth of the global supply of oil is shipped via the Strait of Hormuz.