Iran officially announced on Monday that it had resumed enrichment of uranium at its underground site in Fordow, Politico reports.

The International Atomic Energy Agency (IAEA), which monitors Iran’s nuclear program, confirmed that Tehran had resumed enrichment of uranium to 20 percent, a level not seen since 2015, before the signing of the Joint Comprehensive Plan of Action (JCPOA) between Iran and world powers.

Iranian Foreign Minister Mohammad Javad Zarif wrote on Twitter that the resumption of enrichment was approved by the Iranian parliament and claimed that Iran’s actions are in line with the 2015 nuclear deal.

“Our remedial action conforms fully with Para 36 of JCPOA, after years of non-compliance by several other JCPOA participants. Our measures are fully reversible upon FULL compliance by ALL,” he wrote.

A spokesperson for the State Department criticized the Iranian announcement in a conversation with Reuters, describing it as a form of “nuclear extortion.”

“Iran enriching uranium to 20 percent at Fordow is a clear attempt to increase its campaign of nuclear extortion, an attempt that will continue to fail,” said the spokesperson on condition of anonymity.

Iran’s announcement comes three days after Russia’s ambassador to the IAEA said Iran had told the UN nuclear watchdog it intends to enrich uranium to up to 20% purity.

Iran has gradually scaled back its compliance with the 2015 deal in response to US President Donald Trump’s withdrawal from the agreement in May of 2018.

President-elect Joe Biden has taken a different approach to the Iran deal than Trump and has expressed a desire to rejoin the deal. He recently told The New York Times that he would do so if Iran returned to compliance with it.

The Iranian government, however, has ruled out the possibility of renegotiating the nuclear deal, saying it was fully discussed in detail five years ago and needs no renegotiations.