Donald Trump is expected to withdraw his endorsement of the nuclear deal with Iran next week, leaving its survival uncertain and in the hands of a divided Congress.

Adding to the mood of uncertainty hanging over Washington, Trump used a group photograph before a dinner with military leaders and their spouses to warn cryptically that the evening represented “the calm before the storm”.

When asked by reporters what he meant, the president said: “You’ll find out,” leaving it unclear whether he was referring to impending military action, or whether Trump, a former TV reality show host, was simply creating tension for the sake of it.

White House press secretary Sarah Huckabee Sanders repeatedly declined to clarify Trump’s remarks about “the calm before the storm” on Friday. Speaking to reporters at the White House press briefing, she said “I’m not aware of anything specific that that was in reference to.” But she did cite Iran and North Korea as flashpoints as reporters sought clarification.