Iran said Friday it had enriched uranium at 60% purity for the first time, a move that comes in response to an attack on its main nuclear facility, and which has complicated ongoing talks between Tehran and international powers in Vienna to revive a 2015 nuclear accord. “I proudly announce that at 00:40 this morning, young Iranian scientists… achieved uranium of 60% purity,” Iranian parliament speaker Mohammad Bagher Ghalibaf said, according to state media.

The head of Iran’s nuclear agency, Ali Akbar Salehi, confirmed the step to state television, saying Iran was now producing nine grams of 60%-enriched uranium per hour. Tehran’s latest acceleration of its nuclear program beyond the limits of the 2015 deal comes after it accused Israel of attacking its Natanz nuclear facility on Sunday, causing a blackout that destroyed a number of centrifuges used to enrich uranium. Israel hasn’t commented directly on the allegation, as per official policy.

Although the actual amount of 60%-enriched uranium that Iran is able to produce will be small initially, Western officials worry that the process of enriching closer to weapons grade of 90% purity will allow Iranian scientists and engineers to gain new insight into a critical building block in creating a nuclear weapon.