Israel urged international countries on Thursday to cease nuclear talks with Iran immediately, citing a U.N. watchdog report indicating Tehran had begun generating enriched uranium using more modern centrifuges.

“Iran is using nuclear blackmail as a negotiating tactic, and this should be met with an immediate halt to negotiations and the implementation of tough measures by the world powers,” Prime Minister Naftali Bennett’s office quoted him as saying during a phone call with US Secretary of State Antony Blinken.

The International Atomic Energy Agency (IAEA) said on Wednesday that Iran has begun the process of enriching uranium to up to 20% purity with a cascade of 166 modern IR-6 machines at its Fordow site, which is carved into a mountain.

Iran and major powers are trying, in talks in Vienna, to revive a 2015 deal under which Tehran limited its nuclear programme in exchange for relief from U.S., EU and U.N. economic sanctions. The United States withdrew from the pact in 2018, during the administration of then-President Donald Trump, and Iran responded by violating the agreement’s limits.

An Israeli official said Bennett told Blinken of his objections to any lifting of sanctions against Iran, particularly under an interim deal, which would effectively mean “the massive flow of funds to the Iranian regime”.

Under the 2015 deal, no uranium enrichment is supposed to be carried out at Fordow at all. Until now Iran had been producing enriched uranium there with IR-1 machines and had enriched with some IR-6s without keeping the product.

In a video interview on Thursday with Israel’s YNet news website, Defense Minister Benny Gantz voiced confidence that U.S. President Joe Biden would make good on a promise not to let Iran obtain nuclear weapons.

“I don’t think we are alone. I do think we always have to prepare the option for the moment when we may find ourselves alone,” he said. “I say again, an attack (on Iran) is an option. It doesn’t have to be the first one.”