London Saturday advised British ships to avoid the Strait of Hormuz for "an interim period" following Iran's seizure of a British-flagged oil tanker.
"We remain deeply concerned about Iran's unacceptable actions which represent a clear challenge to international freedom of navigation," a government spokeswoman said following an overnight meeting of the government's COBRA emergencies committee to discuss the crisis.
"We have advised UK shipping to stay out of the area for an interim period."
She noted comments by Foreign Secretary Jeremy Hunt earlier that "there will be serious consequences if the situation is not resolved".
She added that there will be further meetings over the weekend and "we remain in close contact with our international partners".
Iran's Islamic Revolutionary Guard Corps said on Friday it had seized the British-flagged Swedish-owned Stena Impero in the Strait of Hormuz for breaking "international maritime rules".
Iranian authorities alleged Saturday the ship had collided with a fishing boat. It said the tanker was now at anchor off the port of Bandar Abbas with all its crew aboard.