Britain, France and Germany are to mount a last-ditch effort to dissuade Iran from effectively quitting the nuclear deal, warning time was running out for negotiations and the risk of war in the region “has not been averted”.

The diplomatic offensive includes a forthcoming visit by the UK’s new Middle East minister, Andrew Murrison.

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Iran has threatened to take fresh steps to leave the deal on 27 June by breaching enriched uranium limits set out in the 2015 agreement. Officials from the three EU states, which support the deal, will also meet with China and Russia to discuss the situation.

The French foreign minister, Jean-Yves Le Drian, speaking in Paris alongside his German counterpart, said the two countries wanted to coordinate their efforts to stop Iran’s withdrawal from the deal.

“We want to unify our efforts so there is a de-escalation process that starts,” Le Drian said. “There is still time and we hope all the actors show more calm. There is still time, but only a little time.”

Heiko Maas, Germany’s foreign minister, added: “The risk of war in the Gulf has not been averted. We need to do everything so that it doesn’t come to this. That’s why we are talking to all sides. I was in Iran and we are also talking with the Americans. We need to de-escalate through dialogue. It is a time of ‘diplomacy first’ and that’s what we are committed to.”

Murrison’s visit will be the first by a British minister since the UK claimed its own intelligence showed Iran was behind the recent attacks on tankers in the Gulf.

In Tehran, President Hassan Rouhani said there was no chance Iran would delay the deadline to save the deal, but is waiting on evidence that the EU can keep its side of the bargain by setting up a functioning financial vehicle through which European nations can trade with Iran and avoid US sanctions. It appears as if the EU is racing against the clock to get the proposed measure up and running.

If Iran did breach the uranium limits, the deal, known as the joint comprehensive plan of action, gives both sides time to go into a disputes mechanism before it is declared void.

Rouhani made it clear he was not yet willing to sit with Donald Trump and the US to renegotiate the deal.

He told his cabinet: “Sitting at the negotiating table with someone who continues exerting pressures on the Iranian nation has no meaning but surrendering; if they want negotiation and are sincere, they should pave the ground for it and that sincerity means removal of all cruel sanctions, respecting the Iranian nation and accepting the [ruling] system that has risen to power through people voting.”

The comments came as a rocket hit a site near Basra in neighbouring Iraq used by foreign oil companies, including the US energy firm ExxonMobil. The missile strike wounded three people, and in response the oil company ordered further evacuations of staff out of the country. There have been three previous attacks on US-linked installations in recent days, but no claim of responsibility.

The US evacuated hundreds of diplomatic staff from its Baghdad embassy last month, citing unspecified threats from Iran against US interests in Iraq. In Yemen, the Iranian-backed Houthis have continued their campaign to fire drones into Saudi Arabia, but an attack on Wednesday was intercepted in Yemeni air space.

Analysts, as well as many Arab leaders not aligned to Saudi Arabia, believe Iran may be trying to demonstrate the chaos it can create in the oil industry if the US does not backpedal on economic sanctions.

Q&A Why is the Gulf of Oman so important for shipping oil? Show Hide The strait of Hormuz, which provides passage from the Gulf of Oman to the open sea, is the most important gateway for oil exports in the world. With Iran on its northern shore, and the UAE and Oman on its southern shore, the US Energy Information Administration (EIA) calls it the world’s worst 'chokepoint' In 2016, 18.5m barrels of crude oil were transported each day through the strait of Hormuz, compared with 16m through the strait of Malacca, which runs between the Indonesian island of Sumatra, Malaysia and Thailand, connecting the Indian Ocean with the South China Sea. 5m barrels of crude oil are transported annually through the next largest chokepoint, the Suez canal. Phillip Inman

Meanwhile, US military officials have produced further evidence to support Washington’s claim that Iran was behind last week’s tanker attacks. The US navy displayed limpet mine fragments and a magnet it said it had removed from one of the vessels, noting the mines bore a striking resemblance to Iranian mines.

Iran’s defence minister “categorically rejected” accusations that Tehran was behind the attacks, describing evidence presented by Washington as “unsubstantiated”, the country’s official news agency, IRNA, reported.

Washington has released images and a grainy video it alleges shows Iranians on a patrol boat removing an unexploded limpet mine attached to one of the tankers.

“Accusations levelled against Iran’s armed forces and the published film with regards to the incident [that] happened to the vessels … are unsubstantiated and we categorically reject these accusations,” the defence minister, Brig Gen Amir Hatami, was quoted by IRNA as saying.

“The armed forces and the port organisation were among the first to approach the tankers after the incident for relief operations and they rescued 23 people in the first tanker,” he added.