The Iranian officials, speaking at a news conference, did not give specifics but said monitoring would confirm the breach on Monday. The nuclear accord caps Iran’s uranium enrichment at 3.67 percent — far below the 90 percent needed to produce a nuclear weapon.

A spokesman for the Atomic Energy Organization of Iran said that the increase would help fuel the country’s power plants, adding that preparations for the enrichment would begin “within several hours.” Officials suggested earlier that Iran was looking to enrich uranium up to 5 percent.

Iran’s Foreign Minister, Mohammad Javad Zarif, said on Twitter Sunday that the step was “remedial” but that Iran reserved the right to protect its interests in the face of U.S. sanctions.

“All such steps are reversible” if Europe complies with the deal, Zarif said on Twitter.