the blackout at the Natanz nuclear enrichment plant in Iran, which was reportedly the result of an attack by Israel, and by the responses from Tehran, which have included an attack on an Israeli ship and a vow to begin enhancing uranium enrichment from 20 percent to 60 percent, levels banned under the accord and closer to weapons-grade.

The Iranian moves were criticized in a joint statement from the British, French and German foreign ministers on Wednesday.

“This is a serious development since the production of highly enriched uranium constitutes an important step in the production of a nuclear weapon,” the statement said.

The statement called Iran’s moves “particularly regrettable” when the Vienna meetings had made progress. “Iran’s dangerous recent communication is contrary to the constructive spirit and good faith of these discussions,” it noted.

Iran maintains that its nuclear program is purely civilian.

The German Foreign Ministry said that the main topic of the separate meeting of foreign ministers from the Quad would be Afghanistan. Although France pulled its troops out of Afghanistan years ago, the country remains deeply involved in the Iran talks. The Vienna negotiations are trying to bring both the United States and Iran back into compliance with the accord, from which President Donald J. Trump withdrew in May 2018. In response, Iran began to breach enrichment levels, calling its actions “remedial.”

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