Iran announced on Wednesday that it had begun processing nuclear fuel at a controversial mountain facility, which if confirmed, would accelerate its ability to stockpile material that could be used to make a nuclear weapon.

The move represents the most significant breach by Tehran of the Joint Comprehensive Plan of Action, the 2015 nuclear deal hammered out and enshrined in a UN Security Council Resolution by Iran, the US, the UK, France, Russia, China and Germany.

This week’s move marks the fourth rollback of Iran’s commitment to the terms of the deal this year.

Iran says it now has amassed 500kg of enriched uranium, more than the 300kg limit set by the nuclear deal, and is producing enriched uranium at a rate of six kilograms per day. Around 1,100 kilograms of reactor-grade uranium would be required to produce enough highly enriched fissile material for a single nuclear weapon.

Earlier this week Iran announced that it would double the number of advanced centrifuges it was using for research purposes, potentially accelerating its ability obtain nuclear fissile material.

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

Vowing to right the wrongs of the deal, Donald Trump unilaterally pulled out of the agreement last year and launched a draconian campaign of “maximum pressure” on Iran which has severely damaged the country’s economy.

Iranian state media announced that the country had begun injecting uranium gas at the enrichment facility at Fordow, near the central city of Qom.

The US disclosed the existence of the Fordow facility a decade ago, arguing that the once-secret uranium enrichment plant was evidence of Iran’s intent to build a weapons programme.

Under the terms of the 2015 deal, Iran agreed not to process nuclear material at Fordow until 2031 and would only use the facility for research purposes.

The country’s Atomic Energy Organisation said that it had moved 2,000 kilograms of uranium to the facility under the supervision of the International Atomic Energy Agency (IAEA).

“It was placed at the complex’s feeding hall and the process was observed by inspectors from the IAEA,” said a statement by Iranian nuclear authorities.

The Vienna-based IAEA has yet to confirm the injection of gas or the transfer of nuclear material to Fordow.

Iran’s president, Hassan Rouhani, said the move was reversible, a response to Europe’s failures to circumvent a tough US sanctions regiment and uphold its end of the nuclear deal.

Iran insists its nuclear programme is meant only for peaceful civilian ends.

“Iran’s decision to restart enrichment at Fordow is a very significant and worrying step,” Dr Chen Kane, director of Middle East Nonproliferation Program at the Middlebury Institute of International Studies at Monterey told The Independent.

“One of the more important objectives of the JCPOA was to convert Fordow from uranium enrichment to stable isotope separation facility, which does not include work with nuclear material.

“If Iran [goes back on] this commitment with introducing nuclear material to Fordow, it is a step that is relatively harder to reverse since once nuclear material is fed into a centrifuge you cannot do anything else with it other than enrichment.”

Western officials condemned the latest move.

“Iran’s latest actions clearly contravene the deal and pose a risk to our national security,” UK foreign secretary Dominic Raab said in a statement.

“We want to find a way forward through constructive international dialogue but Iran needs to stand by the commitments it made and urgently return to full compliance.”

Earlier this week, the US imposed fresh sanctions on nine people close to Iran’s supreme leader Ali Khamenei, including his son and the head of the judiciary, on the 40th anniversary of the seizing of the US embassy in Tehran by radicals.

US officials denounced the apparent Iranian move as “nuclear blackmail”, but indicated no retaliatory response.

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“Our view has remained that this is a regime intent on using nuclear material to blackmail and try and extort money from Europe or from the west more broadly,” a senior US official said in press briefing.

But despite the technical significance of Iran’s move, it appeared to make few major waves among western diplomatic corps overwhelmed with overlapping crises across the Middle East and the traumatic turns over Brexit.

The US has applied so many sanctions on Iran that it has few tools short of war to apply pressure. And Europe has so carefully abided by the US sanctions, they have little in the way of incentives they can offer Iran. Russia and China appear intent on protecting Iran at the Security Council.

“This is the logical consequence of the standstill in solving the known problems connected to increasing the JCPOA’s sustainability and ensuring the economical results of implementing this deal, which Iran was counting on,” Russian deputy foreign minister Sergei Ryabkov said.

Meanwhile, Reuters news agency reported that Iran briefly held an inspector working for the UN nuclear watchdog and seized her travel documents.

The sources said the incident occurred at Iran's enrichment site at Natanz last week.