Britain is to join the US in a naval mission to protect oil tankers in the Gulf from seizure by Iran, as London shifted away from plans for a European-led mission that had been proposed by the former foreign secretary Jeremy Hunt.

The announcement by Boris Johnson’s government will involve the UK’s two Royal Navy ships in the Gulf collaborating with two US warships and Hunt’s successor urged other countries to join in.

Dominic Raab, the new foreign secretary, said the UK had to respond to the “increased threat” now. He added: “Our aim is to build the broadest international support to uphold freedom of navigation in the region, as protected under international law.”

France and Germany had indicated they would refuse to join any US-led mission, amid concerns about being too closely aligned to a Trump administration that has pulled out of the nuclear deal and contemplated airstrikes on the country.

Despite that, UK was still hoping that by joining the US other countries would be persuaded to participate. Whitehall sources said “there had to come a point” where countries had to act to secure shipping in the Gulf.

But on Monday those hopes were rebuffed again by Germany’s foreign minister, Heiko Maas, who repeated that his country would not join in a US-led operation: “At the moment the Britons would rather join an American mission. We won’t do that.”

In an attempt to ally German and French concerns, Raab said that the UK “approach to Iran hasn’t changed”. The new government remained committed to de-escalation and to “maintain the nuclear deal”, the minister added.

Meanwhile, Iran accused the US of engaging in “economic terrorism” against its people. The Iranian foreign secretary, Mohammad Javad Zarif, also warned Britain that acting in concert with the Trump administration would bring about a response from Tehran.

During a briefing Zarif accused the US of seeking “to tie the ‘bread’ to ‘politics’” and added: “Britain is an accomplice in US economic terrorism, and this complicity will definitely bring about consequences for them.”

Labour critics asked whether the shift in policy demonstrated by the naval announcement meant Johnson’s government was edging closer to the Trump administration’s Iran policy in terms of economic sanctions.

Lord Wood of Anfield, a Labour peer, said: “The question is: will we thereby effectively be joining the US in their mission to stop all Iranian oil exports, a position which the US strongly adheres to, but the UK and EU oppose.”

The announcement comes more than a fortnight after Iran seized the British-flagged Stena Impero oil tanker, prompting Hunt’s call for a “European-led” mission just days before his defeat in the leadership race by Boris Johnson and his eventual sacking.

With little prospect of the European mission coming together, stretched British forces will soon start working with the US, which has a command and control operation in Bahrain, to accompany tankers passing through the strait of Hormuz.

A fifth of the world’s oil passes through the waterway, bounded to the north by Iran, which has been accused of pursuing a policy of disrupting shipping in an attempt to lift the world oil price to retaliate against US sanctions.

The Iranians seized the Stena Impero partly in response to the impounding of an Iran-flagged oil tanker, the Grace 1, in Gibraltar. Other ships in the Gulf had been sabotaged in recent weeks, damaged by mines above the waterline widely believed to have been planted by Iran’s Revolutionary Guards.

The UK is patrolling the Gulf with two warships, HMS Duncan, a Type 45 Destroyer, which joined HMS Montrose, a Type 23 Frigate, at the end of last month. But when Stena Impero was seized in the strait, the Montrose was unable to intervene because it was 60 minutes’ sail away.

A spokeswoman for the US Department of Defense said: “We welcome the decision of the UK to participate in the international maritime security construct to enhance maritime domain awareness, promote safe passage, and enhance freedom of navigation in the Arabian Gulf, strait of Hormuz, Arabian Sea, and Bab el-Mandeb.”