BRUSSELS/PARIS (Reuters) - Britain’s decision to join a U.S.-led naval mission in the Gulf has delayed European efforts to set up a maritime force to ensure safe shipping in the Strait of Hormuz separate from American patrols, EU diplomats say.

FILE PHOTO: Rafale and Super Etendards fighter jets are parked prior to a mission aboard France's Charles de Gaulle aircraft carrier sailing in the Gulf, January 28, 2016. REUTERS/Philippe Wojazer/File Photo

Britain and France proposed a European-led maritime force in July that was to be independent of the United States. They won support from Denmark, Italy and Spain, who were wary of an American mission for fear of making U.S.-Iranian tensions worse.

The proposal was announced after Iran seized a British-flagged tanker in the Strait, in what was then widely seen as retaliation for the seizure of an Iranian tanker in Gibraltar by British marines. The British-flagged Stena Impero is still being held by Iran, although Tehran has signaled it could release it soon. The Iranian tanker was released from Gibraltar last month.

France will make a fresh attempt on Sept. 16 to set up a mission to protect merchant shipping in the Strait, through which a fifth of the world’s oil passes, hoping to gather some 15 European countries in Paris to discuss a way forward.

But diplomats involved in talks between EU capitals said London’s unexpected change of strategy to join a U.S.-led mission, taken by the new government of Prime Minister Boris Johnson on Aug. 5, has frustrated progress.

“Many of us wanted to do this with Britain, out of European solidarity, and to avoid the U.S. maximum pressure campaign on Iran,” one senior EU diplomat said. “Now it’s all on hold because Britain sided with the Americans.”

IRAN DIVIDES EUROPEANS AND U.S.

Britain, France and Germany, with support from the rest of the EU, are trying to save the 2015 nuclear accord between Iran and major powers, under which Tehran undertook to curb its nuclear program in exchange for the lifting of sanctions.

U.S. President Donald Trump pulled out of the Iran deal in May last year, dividing America from its European allies, who say the accord was stopping Tehran from developing nuclear weapons. Trump has since reinstated crippling sanctions on Iran.

Given Britain’s plans to quit the EU, London initially sought a mission that would not involve the European Union, NATO or the United States directly, but a looser coalition of European nations, including non-EU member Norway.

Iran rejects the proposal and says foreign powers should leave securing shipping lanes to Tehran and others in the region. Saudi Arabia, Iran, the United Arab Emirates, Kuwait and Iraq export most of their crude via the Strait.

A European mission could be run by a French command. France has a naval base in the United Arab Emirates.

“It will be with European partners, who are interested in a European mission that doesn’t give the impression of being a coalition against Iran,” a French defense official said.

Italy, Denmark, Spain, Norway, Belgium and Sweden could yet join France in a European-led mission. The Netherlands is assessing both U.S. and French proposals, but diplomats said it was inclined to join a European-led initiative.

Any mission would still need parliamentary approval in some EU countries, including Denmark and the Netherlands.