Britain will seek to put together a European-led maritime protection mission to ensure safe shipping through the Strait of Hormuz after Iran seized a British-flagged vessel in what London said was an act of "state piracy".
Iran's Revolutionary Guards seized the Stena Impero in the Strait on Friday. British Royal Marines seized an Iranian tanker off the coast of Gibraltar two weeks ago.
"Under international law Iran had no right to obstruct the ship's passage - let alone board her. It was therefore an act of state piracy," Foreign Secretary Jeremy Hunt told parliament.
"We will now seek to put together a European-led maritime protection mission to support safe passage of both crew and cargo in this vital region," Hunt said.
He said Britain has had constructive discussions with a number of countries in the last 48 hours over the mission.
He also said he would discuss how this would complement U.S. proposals in the area but that Britain would not join the U.S. plan as it wanted to preserve the nuclear deal.
"It will not be part of the US maximum pressure policy on Iran because we remain committed to preserving the Iran nuclear agreement," Hunt said.
Britain will now ask all British-flagged ships to give the government notice of intentions to pass through the Strait of Hormuz, Hunt said.
"We will then advise them as to the safest way to transit, which may involve travelling in convoy," Hunt said, adding that Britain would also strengthen measures to protect ships flying the flags of other countries but which had British crew.
"It is of course not possible for the Royal Navy to provide escorts for every single ship or indeed eliminate all risks of piracy," Hunt said.
"But the risks can be substantially reduced if commercial shipping companies cooperate fully with instructions from the Department of Transport, which we strongly encourage them to do." (Reporting by Kylie MacLellan and Guy Faulconbridge, Editing by Alistair Smout)