WASHINGTON — As he had been signaling for weeks, President Donald Trump announced Friday that he would not be certifying that the 2015 Iran nuclear deal meets congressional requirements, though he stopped short of withdrawing the United States from the arms control pact. Instead, Trump said he was urging Congress to amend legislation overseeing the deal to also target Iran’s ballistic missile program and threaten sanctions if Iran expands its enrichment capacity when certain provisions in the accord “sunset,” permitting it to do so after a decade.

The widely anticipated decision to withhold certification, over technical legislative grounds rather than any claim that Iran was not abiding by the accord, gives Congress 60 days to decide if it will reimpose US nuclear-related sanctions suspended under the deal in return for Iran’s rollback of its nuclear program.

European leaders expressed alarm at the step, and several members of Congress, including some who opposed the deal two years ago, said Trump had defied the recommendation of his own top generals and advisers in putting the fate of a nuclear deal that they concede is working into uncertainty.

“President Trump’s own secretary of defense and chairman of the Joint Chiefs of Staff, Gens. [James] Mattis and [Joseph] Dunford, both said that it’s in our national security interest to keep the [Joint Comprehensive Plan of Action (JCPOA)] in place and I agree,” Senate Minority Leader Chuck Schumer, D-N.Y., who voted against the deal in 2015, said in a statement Friday. “I believe Congress, both Democrats and Republicans, will heed their recommendation.”