The White House has condemned Iran’s ‘blackmail’ after Tehran warned it would break uranium stockpile limits in retaliation for the oil tanker accusations.

A US National Security Council spokesman said today: ‘President Trump has made it clear that he will never allow Iran to develop nuclear weapons. The regime’s nuclear blackmail must be met with increased international pressure.’

The American response comes after Iran’s atomic energy agency said they would ramp up their output to near weapons-grade levels within ten days.

Behrouz Kamalvandi, of the atomic energy agency, said uranium enrichment levels would soar to 20 per cent from the current 3.67 per cent and would only be reversed if other parties in the Iran Deal ‘lived up to their commitments.’

It comes after Washington blamed Iran for attacks on two oil tankers in the Gulf of Oman last week, almost exactly a month after similar attacks which were also blamed on the country.

French president Emmanuel Macron urged Iran to be ‘patient and responsible’ with the Obama-era pact as EU foreign ministers look to salvage the crumbling agreement.

Israeli Prime Minister Benjamin Netanyahu said it was vital that ‘snapback sanctions’ were imposed should Iran plough ahead with uranium enrichment. 

Behrouz Kamalvandi (left), Iran’s spokesman for its nuclear energy agency, said that Iran will breach the nuclear pact signed with the Obama White House by June 27

It comes after fresh attacks against two oil tankers in the Gulf of Oman last week which Washington has blamed on Tehran

British Foreign Secretary Jeremy Hunt has backed the Americans in saying Tehran was ‘almost certainly’ behind the attacks. 

‘Today the countdown to pass the 300 kilogrammes reserve of enriched uranium has started and in 10 days time… we will pass this limit,’ Kamalvandi said. 

The move ‘will be reversed once other parties live up to their commitments,’ he added, in an apparent reference to the nuclear treaty. 

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How is uranium enriched to weapons-grade levels? 

Enriching uranium means boosting its concentration of an isotope called U-235, which powers nuclear reactions, and stripping out another unwanted isotope called U-238. 

When uranium is mined, it typically has about 140 atoms of the unwanted isotope U-238 for every atom of U-235. 

Refining it to a purity of 3.67 per cent, the level now allowed by the nuclear deal, means removing 114 atoms of U-238 for every atom of U-235.

Boosting its purity to 20 per cent means removing 22 more unwanted isotopes per atom of U-235, while going from there to 90 per cent purity means removing just four more per atom of U-235, he noted. 

Ninety percent is considered weapons-grade material.

That means going from 20 per cent to 90 per cent is a relatively quicker process than going from 3.67 per cent to 20 per cent.

Monday’s announcement brings forward a July 7 deadline that Tehran had set to salvage the nuclear deal after Donald Trump tore up the pact a year ago.  

Tehran had asked European signatories – including France , Germany  and Britain – to guarantee it the economic benefits it was promised under the deal or it would stop complying.

Diplomats including Germany’s foreign minister had travelled to Tehran in hopes of salvaging the deal – but after Washington imposed fresh sanctions on Iran it made those efforts all-but impossible.

Kamalvandi said on Monday that it is not too late for the nuclear deal ‘if European countries act’, warning that they will not get another chance to do so. 

He added that Iran will enrich uranium to ‘any level’ depending on the country’s needs, and that it currently needs uranium enriched to 5 per cent and 20 per cent.

Under the deal, Tehran only enriches uranium to 3.67 per cent, the minimum level needed to fuel a nuclear power station. 

Kamalvandi said Monday that the country needs 5 per cent enrichment for its nuclear power plant in southern Iranian port of Bushehr and 20 per cent enrichment for a Tehran research reactor. 

Weapons-grade uranium is enriched to 90 per cent, but going from 20 per cent to 90 per cent is a much quicker process than going from 3.67 per cent to 20 per cent. 

Enriching to any level above 3.67 per cent would put Iran in breach of the pact forged under the Obama administration. 

The US has released video which it claims shows an Iranian boat removing a limpet mine from the side of one of the vessels in an attempt to hide evidence

Iran will breach uranium stockpile limits set in the deal after quadrupling its output and will begin enriching uranium up to 20 per cent, just one step away from weapons-grade level (pictured, Iran's nuclear power plant in Bushehr)

Iran will breach uranium stockpile limits set in the deal after quadrupling its output and will begin enriching uranium up to 20 per cent, just one step away from weapons-grade level (pictured, Iran’s nuclear power plant in Bushehr)

Kamalvandi’s comments come in the wake of suspected attacks on oil tankers last week in the region that Washington has blamed on Iran. 

In the face of scepticism, US Secretary of State Mike Pompeo said on Sunday that there is no disputing the evidence gathered by American intelligence agencies.

The US has released a video which it claims shows an Iranian boat removing two limpet mines from one of the tankers in an attempt to hide evidence.

‘I wouldn’t have said it if the intelligence community hadn’t become convinced that this was the case,’ Pompeo told CBS on Face the Nation Sunday morning.

‘I will concede there are countries that just wish this would go away, and they want to act in a way that is counterfactual,’ he added.

Germany's foreign minister Heiko Maas said that Germany has still not decided who is to blame for the tanker attack, ahead of a meeting of European foreign ministers

Germany’s foreign minister Heiko Maas said that Germany has still not decided who is to blame for the tanker attack, ahead of a meeting of European foreign ministers 

A fireball erupted on the Norwegian-owned MT Front Altair after a suspected torpedo attack caused three explosions, forcing the crew to abandon ship.

Sailors on the Japanese-owned Kokuka Courageous also had to flee after it was hit by another explosion, in a pair of attacks which left the Middle East on high alert. 

Tehran has said it is ‘suspicious’ about the timing of the explosions during a visit by Japan’s leader Shinzo Abe, and implied that Washington may have staged the attack to justify increased hostility in the region.

On Monday Heiko Maas, Germany’s foreign minister, stressed that his country has not yet made up its mind about who was behind the tanker attacks.

Maas said Germany and others need a clearer picture before wading into a diplomatic conflict which could have serious implications in the Middle East.

He added that U.S. and British intelligence needs to be compared with other information from allies. ‘We have to be very careful,’ he said.

EU foreign policy chief Federica Mogherini said it was not a time to jump to action without proper information.

‘The maximum restraint and wisdom should be applied,’ she said ahead of the monthly foreign ministers meeting in Luxembourg.