Washington —  US officials announced new sanctions against Iran on Monday and insisted that a raft of nuclear-related restrictions are back in force, part of a standoff with European allies that’s spurring a crisis at the UN Security Council.

Secretary of State Michael Pompeo said that all UN members are expected to enforce sanctions suspended under a 2015 nuclear deal now that the US has declared Tehran in violation of the agreement and invoked what is known as a “snapback” of the restrictions. Thirteen of the 15 members of the Security Council have said they would not recognise the move because the Trump administration quit the multinational deal in 2018...