TEHRAN/JEDDAH: Iran’s President Hassan Rouhani said Wednesday Tehran’s decision to boost uranium enrichment to 60 percent was a response to Israel’s “nuclear terrorism,” three days after an attack on its Natanz nuclear facility.

“Enabling IR-6 (centrifuges) at Natanz today, or bringing enrichment to 60 percent: this is the response to your malice,” Rouhani said in televised remarks. “What you did was nuclear terrorism. What we do is legal.”

The new move casts a cloud over talks in Vienna aimed at reviving Iran’s 2015 nuclear deal with major powers, after former US President Donald Trump abandoned it three years ago.

Enriching uranium to 60 percent from Iran’s current 20 percent would take the fissile material closer to the 90 percent required to make a nuclear bomb. Iran’s chief nuclear negotiator Abbas Araqchi also said it would activate 1,000 advanced centrifuge machines at Natanz, which was crippled on Sunday by an explosion that knocked out its power supply. Israel’s Mossad spy agency is thought to have been behind the attack.

The blast at the underground Natanz plant was a “very bad gamble” that would boost Tehran’s leverage in the talks to salvage the nuclear deal, which resume on Thursday in Vienna, Iranian Foreign Minister Mohammad Javad Zarif said.

“I assure you that in the near future more advanced uranium enrichment centrifuges will be placed in the Natanz facility,” he said.

The Vienna talks began last week, when Iran and other signatories to the 2015 Joint Comprehensive Plan of Action (JCPOA) held what they described as “constructive” discussions about salvaging the deal, which collapsed when Trump reimposed economic sanctions on Tehran and Iran began breaching its limits on uranium enrichment.

Trump’s successor, Joe Biden, has said he will ease sanctions when Iran returns to compliance with the deal. Iran insists sanctions must be lifted first. In addition, Israel and US allies in the Gulf oppose any revived agreement that does not address Iran’s ballistic missile program and its regional meddling through proxy militias in Yemen, Iraq and elsewhere.

The JCPOA had capped the level of purity to which Iran can enrich uranium hexafluoride, the feedstock for centrifuges, at 3.6 percent, far below the 90 percent needed for bomb-grade material.

Iran in recent months has raised enrichment to 20 percent purity, a level at which uranium is considered to be highly enriched and is a significant step toward weapons grade. Civilian nuclear power plants, which Iran claims are its only objective, only require enrichment to between 3 percent and 5 percent.

The biggest obstacle to producing nuclear weapons is accumulating sufficient quantities of fissile material, either 90 percent enriched uranium or plutonium, for the core of a bomb. Western intelligence services believe Iran had a clandestine nuclear weapons program that was suspended in 2003.