ISTANBUL — Iran's parliament speaker said Friday that Tehran has successfully enriched uranium to 60 percent purity, its highest level yet, in a move that the United States and its European allies warned would complicate efforts to revive a nuclear deal between Iran and world powers.

In a Twitter message, Mohammad Bagher Ghalibaf said that at 12:40 a.m. Friday, “young and pious Iranian scientists were able to obtain a 60 percent uranium product.”

“I congratulate the brave people of Islamic Republic of Iran on this success,” he added. “The will of the Iranian people is miraculous and will thwart any conspiracy.”

Ali Akbar Salehi, head of Iran’s nuclear energy agency, later confirmed that 60 percent enrichment was underway at the Natanz nuclear facility and cited an output of nine grams per hour, according to Iranian news agencies.

Iran’s government vowed earlier this week that it would increase enrichment from the current top level of 20 percent, in what officials cast as retaliation for a suspected Israeli attack days earlier on Natanz. The announcement seemed to add a new obstacle to multilateral negotiations underway in Vienna aimed at restoring the 2015 nuclear deal between Iran and six world powers.

Israel has not commented on the Natanz attack, which Iran said damaged centrifuges and caused a fire.

Iran began breaching the terms of the deal after President Donald Trump withdrew from the accord in 2018. In January, Iran began enriching uranium from the 3.67 concentration allowed under the deal to 20 percent — a step closer to the 90 percent required for the fissile material in a nuclear weapon.

Iran has said it is not seeking to build a nuclear weapon, and a U.S. intelligence report released earlier this week determined that Tehran was not “currently undertaking” activities needed to produce such a weapon.

In Washington, President Biden said Iran’s enrichment push is “contrary to the agreement,” but noted that U.S. and Iranian envoys remain “engaged in indirect discussions.”

Despite dire predictions about the impact of recent events on the Vienna talks, Abbas Araghchi, Iran’s lead negotiator, said in an interview with Iran’s Press TV on Thursday that they remained “on a good track, although we had the negative impacts of the last days’ developments.”

His delegation is seeking a sweeping repeal of sanctions that were reimposed by the Trump administration after it withdrew from the deal — as well as more than 1,500 new sanctions that Trump imposed — in return for Tehran’s agreement to resume compliance with the accord.

In Vienna, working groups were convened to conduct the difficult work of outlining “concrete, specific measures” to be taken by Iran and the United States to move forward, Araghchi said. “If there is good faith on the U.S. side,” he added, “the way is quite clear.”