The president tweeted the news on Monday, previewing a White House announcement scheduled for 2 pm local time.
The president had given European powers until May 12 to come up with “fixes” to the deal’s most controversial provisions. That’s the date by which he is required to inform Congress whether he will waive nuclear sanctions on Iran lifted by the landmark accord.
French, German and British leaders have visited Washington in recent weeks to plea for the US president to remain within the accord. But US officials say he is likely to withdraw, throwing the entire agreement in doubt.
Israeli officials are pushing for Trump to pull out, but advocates of the deal say that such a move will remove checks on Iran in its pursuit of material critical to nuclear weapons.
European diplomats said privately they expected Trump to effectively withdraw from the agreement, which was struck by six major powers — Britain, China, France, Germany, Russia and the United States — and Iran in July 2015.
"It's pretty obvious to me that unless something changes in the next few days, I believe the president will not waive the sanctions," one European diplomat said, adding he saw only a "very small" chance that Trump stays in the deal.
European leaders have warned that Trump's withdrawal would strike a blow to the alliance between Western Europe and the United States, and undo years of negotiations that they say were successful in halting Iran's nuclear ambitions.
Reuters contributed to this report.