The United Kingdom, France and Germany expressed their “grave concern” in a statement over Iran’s plan to ramp up uranium enrichment, a move the European powers warned would undermine the fragile diplomatic process as the Joe Biden administration seeks to revive the nuclear agreement.

“This is a serious development since the production of highly enriched uranium constitutes an important step in the production of a nuclear weapon,” the European statement said. “Iran has no credible civilian need for enrichment at this level.”

Iran on Tuesday said it would begin enriching uranium at 60% purity using advanced centrifuges, in retaliation against a suspected Israeli attack on its Natanz underground nuclear facility.

The higher enrichment — three times the current level — would represent a significant breach of the nuclear deal but fall short of the 90% Iran would need to build a bomb. The attack on Sunday, which according to an Iranian lawmaker damaged or destroyed several thousand centrifuges, likely set back Iran’s ability to enrich uranium by many months, although the full extent of the damage isn’t known.