Iran has suggested it could boost its enrichment of uranium to 20 per cent purity, a level that alarms nuclear arms specialists because it is considered a relatively easy jump to weapons-grade material.

“If Iran decides, it can have 20 per cent enriched fuel within one to two days,” the Fars news agency quoted Behrouz Kamalvandi, spokesman of Iran’s Atomic Energy Organization, as saying.

The comment came two days before a much-anticipated deadline set by Tehran for the latest escalation of its nuclear programme in response to crippling sanctions imposed by the US following its withdrawal from the 2015 nuclear deal, the Joint Comprehensive Plan of Action (JCPOA).

Diplomats were on edge as Iran prepares to announce a possible escalation of its nuclear programme on Thursday, with the French president, Emmanuel Macron, scrambling to come up with a deal to salvage the JCPOA.

The US president, Donald Trump, withdrew from the deal in 2018 and imposed a policy of “maximum pressure” on Iran to convince it to come back to the negotiating table. But in some of his bluntest remarks yet, Iran’s president Hassan Rouhani ruled out any direct talks with the White House.

Tensions high as Trump approves new Iran sanctions: In pictures Show all 17 1 /17 Tensions high as Trump approves new Iran sanctions: In pictures Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, their surface-to-air missile is seen as it shoots down a US surveillance drone EPA Tensions high as Trump approves new Iran sanctions: In pictures This photo shows US RQ-4A Global Hawk unmanned surveillance drone. A drone of this model was shot down by Iran on Thursday 21 June AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures An oil tanker is on fire after it was subject to a suspected attacked at the Gulf of Oman on June 13. The US has blamed Iran for the attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures US President Trump holds up a signed executive order to increase sanctions on Iran on 24 June AP Tensions high as Trump approves new Iran sanctions: In pictures Iranian President Rouhani stated in a televised address that the White House is "afflicted by mental retardation" following the increase in sanctions on 25 June EPA Tensions high as Trump approves new Iran sanctions: In pictures An Iranian navy boat tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures A screenshot from a video released by the US Department of Defense that the US claims to show Iranian removing an unexploded limpet mine form the hull of the Japan-owned ship that was attacked in the Gulf of Oman on June 13 Getty Tensions high as Trump approves new Iran sanctions: In pictures An item reportedly found on the Japan-owned oil tanker that was attacked on June 13 in the Gulf of Oman AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures A handout photograph from the US Department of Defense shows a composite material that the US claim was left behind on the hull of the Japan-owned oil tanker following the removal of an unexploded limpet mine Getty Tensions high as Trump approves new Iran sanctions: In pictures A view from the cabin of an Iranian navy boat as it tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack EPA Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The picture suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The pictures suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack EPA

Mr Trump and Mr Rouhani last week suggested they were open to such talks. But in a speech on Tuesday, Mr Rouhani said any negotiations with the US would only be possible with other world powers and only after the US lifts “all” sanctions on Iran imposed since Mr Trump last year pulled out of the JCPOA, the landmark nuclear signed by his predecessor, Barack Obama.

“The issue of bilateral talks is not on the agenda in principle,” Mr Rouhani told parliament. “We have no plans for bilateral talks with America and have never had.”

It was unclear whether Mr Kamalvandi was suggesting Iran was pondering a move to boost its small stockpile of 20 per cent enriched uranium as a response to the US sanctions, whether he was showing off about Iran’s technical capabilities, or leaving just enough ambiguity to put pressure on European countries seeking to come up with a scheme that would prevent Iran from making any drastic moves.

Tehran has already increased its stockpile of the material and boosted its level of enrichment as a response to US sanctions which have crippled Iran’s ability to sell its oil.

Mr Macron has spent hours this week speaking to Mr Rouhani on the phone, and reports suggest he is offering Iran $15bn in credits in exchange for its full compliance with the JCPOA, which gave Iran economic incentives to place limits on its nuclear programme.

“Today the essence of our talks with the European countries is this that if they purchase our oil for cash or credit, or make advance purchases and let us access the money for it, this will make conditions easier for us to halt the steps for rolling back our commitments for as long as such conditions are in place,” said Mr Rouhani.

Even if Iran escalates its nuclear programme on Thursday, Mr Rouhani said it would it still be open to talks with the remaining JCPOA partners, including the UK, Russia, Germany, France, and China.

But Mr Rouhani insisted that his earlier remarks saying he was open to talks with the US had been misunderstood.

“If America lifts all of its sanctions – I believe it does not matter whether it returns to the JCPOA, what is important is the sanctions – there still is a chance for America to attend meetings ... like in the past,” he said. “But this will only be possible provided that it lifts all sanctions.”

Donald Trump and Hassan Rouhani suggest they could meet to resolve US-Iran crisis

Despite economic hardships caused by Washington’s sanctions, Iran continues to refine its conventional weapons programme and support armed allies across the Middle East, posing a challenge to the US and its allies as well as the UK and France.

Upping its nuclear programme may cause the collapse of the JCPOA, but Tehran may calculate it can count on China and Russia, both veto-wielding members of the UN Security Council, to shield it from punishment.

“We share the view that the situation which has taken shape surrounding the JCPOA is a direct consequence of the destructive steps taken by the American administration which withdrew from the agreement,” Russian foreign minister, Sergei Lavrov, said during a meeting with his Iranian counterpart, Mohammad Javad Zarif, on Monday.

In a further escalation of tensions, the Iranian oil tanker Adrian Darya 1 at the centre of a dispute between Tehran and western powers appeared to have turned off its transponder in the Mediterranean west of Syria yesterday.

The tanker which is loaded with Iranian crude oil, sent its last signal giving its position between Cyprus and Syria sailing north at 15:53 GMT on Monday, Refinitiv ship-tracking data showed.

The vessel, formerly named Grace 1, was detained by British Royal Marine commandos off Gibraltar on 4 July as it was suspected to be en route to Syria in violation of EU sanctions.