Prime Minister Benjamin Netanyahu of Israel displayed satellite photographs that he said showed the site, and he called upon other countries to join the United States in maintaining pressure on Tehran.
"Unfortunately the European parties have failed to fulfil their commitments... The deal is not a one-way street and Iran will act accordingly as we have done so far by gradually downgrading our commitments," said Ali Akbar Salehi, director of Iran's nuclear energy agency.
President Hassan Rouhani of Iran had earlier signaled that the country’s atomic energy agency had been “ordered to immediately start what is needed in the field of research and development, and abandon all the commitments that were in place,” according to Iranian news accounts.
Tensions began to rise in May 2018 after President Donald Trump unilaterally withdrew the United States from the 2015 Joint Comprehensive Plan of Action (JCPOA) agreement, commonly referred to as the Iran nuclear deal, and reimposed US sanctions on Tehran.
Britain, France, Germany, Russia, China and Iran have been trying to salvage the pact since the United States withdrew from it in May 2018 and re-imposed and toughened sanctions on Iran, crippling an already weak economy.
The two threats would reverse major achievements of the agreement, although Iran omitted important details about how far it might go to returning to the status quo before the pact, when Western experts believed it could build a bomb within months.
The steps Iran has taken are all easily reversible. Yet the new move Iran said it was taking Sunday — to increase enrichment levels beyond the 3.67% purity that is the ceiling under the deal — is the most threatening.
President Donald Trump, who campaigned on a promise of tearing up the deal because it didn't address Iran's ballistic missile program or its involvement in regional conflicts, withdrew America from the accord in May 2018.