Iran announced Tuesday it would resume operating centrifuges at its landmark underground nuclear facility, taking the most provocative step so far in its strategy of slowly violating the 2015 nuclear agreement in protest at US sanctions.

Hassan Rouhani, Iran’s president, said his country would begin injecting gas into 1,044 centrifuges at Fordow, a nuclear centre carved into a mountain which has long worried Western and Israeli officials as a potential site for bomb development.

The nuclear agreement forbids any uranium enrichment at Fordow, which Iran kept hidden from the world until 2009. Mr Rouhani acknowledged the move was likely to cause alarm but said Iran would reverse it if the deal’s other signatories complied with the agreement.

“We know their sensitivity with regard to Fordow,” he said. “But at the same time when they uphold their commitments we will cut off the gas again.”

It was not immediately clear if Iran was resuming uranium enrichment at Fordow or merely injecting gas back into the centrifuges. Both steps would be a breach of the nuclear deal but a full-scale resumption of uranium enrichment would be a much more significant step.