In this Sunday, July 21, 2019 photo, a speedboat of the Iran's Revolutionary Guard moves around a British-flagged oil tanker Stena Impero which was seized in the Strait of Hormuz on Friday by the Guard, in the Iranian port of Bandar Abbas. Image Credit: AP

London - Britain on Monday ruled out swapping seized oil tankers with Iran as a second UK warship arrived in the Gulf to conduct convoys that have irritated Tehran.

A sense of crisis in the world’s busiest oil shipping lane has been building up for weeks as Iran responds to US President Donald Trump’s “maximum pressure” campaign.

The US economic sanctions and stepped-up military presence are designed to force Iran to renegotiate a landmark 2015 nuclear pact from which Trump pulled out last year.

Britain seized one of Iran’s tankers - the Grace 1 - on July 4 on suspicion of it carrying oil to Syria in violation of EU sanctions.

Freedom of navigation in the Strait of Hormuz is vital not just to the UK, but also our international partners and allies.

- Ben Wallace, UK Defence Secretary

Iran vowed to retaliate and its Revolutionary Guards stormed and detained the UK-flagged Stena Impero and its 23 crew as they sailed through the Strait of Hormuz on July 20.

New British Foreign Secretary Dominic Raab flatly rejected the idea of the two tankers being exchanged or simultaneously released in a bid to dial back the tensions.

“There is no quid pro quo,” Raab told BBC radio.

“This is not about some kind of barter. This is about international law and the rules of the international legal system being upheld,” he said.

“That is what we will insist on.”

Iranian President Hassan Rouhani had hinted earlier that he was open to a tanker swap.

Iran said on Sunday that its ship’s seizure was also a violation of the 2015 nuclear pact that Britain co-signed and is trying to keep alive with EU allies.

“Freedom of navigation in the Strait of Hormuz is vital not just to the UK, but also our international partners and allies,” UK Defence Secretary Ben Wallace said.

Yet Britain’s European force proposal is running up one already being prepared by the United States.

Both plans have strongly angered Tehran.

Britain’s Raab said London was still insisting on a European force - despite the potential conflict with Washington.

“This shouldn’t be some sort of geopolitical, EU versus US tussle,” he said in the radio interview.

“It should be (about) what puts us in the best position with the widest group of international actors to uphold the rule of law.”

He added that “it would be important for the European-led initiative to have US support to make it viable”.