Iran will begin enriching uranium to 60 percent purity, a top official said Tuesday, far exceeding its current level, in a defiant move following an attack on one of its key nuclear sites, Iranian news agencies reported. Iran’s state-run Press TV quoted Iran’s lead nuclear negotiator, Abbas Araghchi, as saying the country informed the International Atomic Energy Agency of plans to start 60 percent uranium enrichment.

The announcement puts Iran closer to weapons-grade levels of more than 90 percent enrichment and exceeds its current top level of 20 percent. The move adds another major hurdle to negotiations to revive a 2015 nuclear deal negotiated between Iran and six world powers.

Talks were set to reconvene in Vienna later this week between Tehran and the world powers, including the United States. Iran began breaching the accord after President Donald Trump withdrew from the deal in 2018, reimposed the sanctions on Tehran that were lifted under the agreement, and added more than 1,500 additional measures in what his administration called a “maximum pressure” campaign to cripple the Iranian economy.