Iran has begun injecting uranium gas into centrifuges at its Fordow nuclear facility with plans to evenutally be fully operational, the country's president has said.
Hassan Rouhani tweeted his "thanks to US policy and it's allies" on Wednesday over the decision to take a further step back from the international nuclear treaty signed in 2015.
"Iran's 4th step in reducing its commitments under the [Joint Comprehensive Plan of Action (JCPOA)] by injecting gas to 1,044 centrifuges begins today," he wrote.
"Thanks to US policy and its allies, Fordow will soon be back and operational."
Iran has been gradually moving further away from the stipulations listed in the deal since the US pulled out entirely last year.
The US later went on to impose strict sanctions on Iran, which have crippled the country's economy.
Meanwhile on Wednesday, nuclear inspectors with the International Atomic Energy Agency (IAEA) said they were on the ground in Iran and would be reporting back on relevant activity.
"We are aware of the media reports today related to Fordow," an IAEA spokesperson said. "Agency inspectors are on the ground in Iran and they will report any relevant activities to IAEA headquarters in Vienna."
Enrichment of 5% versus 20%
The news on Wednesday came hours after Iranian nuclear chief Ali Akbar Salehi said the country would begin to enrich unranium to a 5% purity level, which is 1.37% higher than what was agreed in the deal.
He went on to add that Iran had the capabilities to reach a 20% purity level, if necessary.
To put this into context, nuclear reactors generally use enriched uranium at a level between 3-5% purity.
Any concentration below 20% is also considered a low-enriched uranium (LEU), while anything higher is a highly-enriched uranium (HEU).
How much is needed for a nuclear bomb?
In order to reach a level considered weapons-grade, the purity would need to be around 80-90%.
It is still possible to create a nuclear weapon with a lower concentration than this, but the weapon would be much larger, heavier and difficult to move.
However — don't be fooled by the seemingly huge gap between 20% and 80% enrichment.
The most laborious part of the enrichment process is actually situated between the 0-20% purity level, due to a larger number of undesirable atoms that need to be extracted.
But once 20% is reached, the enrichment process to 90% is then boosted quite rapidly.
- How much enriched uranium is needed for a nuclear weapon?
- Iran to inject uranium gas into its centrifuges in latest step back from deal
A number of fellow signatories on the 2015 treaty have since expressed their alarm over Iran's latest announcement, having worked to try and salvage the agreement since the US pulled out.
Russian Foreign Minister Sergei Lavrov said the developments were extremely alarming, but expressed an understanding for Iran's behaviour and placed the blame in the hands of the US.
Meanwhile, French President Emmanuel Macron said the situation was "grave", and that it demonstrated Iran's "explicit and blunt manner" to withdraw from the JCPOA.
Speaking at the end of his three-day state visit to China, Macron said: "I think that for the first time, Iran has decided in an explicit and blunt manner to leave the JCPOA agreement, which marks a profound shift."
The US has also expressed it's concern, with a state department spokesperson saying on Wednesday that the latest move marked a "big step in the wrong direction."
They later reiterated the US's support for the IAEA's role in observing Iran's nuclear activity.