State Department officials initially suggested it could come as early as Thursday, but later said it would not happen before Friday.
"You're going to be finding out very soon".
But they said he might also impose new, targeted sanctions on Iranian businesses and people allegedly involved in missile tests, supporting terrorism, and human rights abuses.
"I am expecting new sanctions on Iran", Treasury Secretary Steven Mnuchin told reporters Thursday.
Mr Zarif noted in a tweet the "strong consensus in Brussels" that Tehran is respecting its obligations and that "Iran's continued compliance [is] conditioned on full compliance by the United States".
Despite the nuclear deal, most USA trade with and investment in Iran is banned under separate US sanctions for its human rights abuses, ballistic missiles and support for terrorism.
The US Congress requires the president to periodically certify Iran's compliance and issue a waiver to allow U.S sanctions to remain suspended.
Such a balance could satisfy Trump's demand to raise pressure on Iran, while not embarking on a frontal assault on the most central trade-offs of the nuclear agreement.
ISRO successfully launches 100th satellite, first mission after IRNSS-1H failure
The Indian satellites are 710 kg Cartosat-2 series for earth observation, a 100 kg micro satellite and a 5 kg nano satellite. PSLV-C40 will be launched from the first launch pad of the Satish Dhawan Space Centre, Sriharikota on Friday at 9.29 am.
Measures to isolate and pressure Iran partly "by spotlighting human rights abuses, corruption, support to terrorism and militant proxies, progress on their ballistic missile program, which is still subject to United Nations sanctions - all of that can be undertaken right away", Juan Zarate, a former assistant secretary for terrorist financing and financial crimes at the Treasury Department, said during a congressional hearing Wednesday. European countries are banking on the deal, as many began investing in Iran after the sanctions were lifted.
Retired US military officers, members of the US Congress and former US ambassadors were among 52 US national security experts who signed a letter released on Monday urging Trump not to jeopardize the deal with Iran. "Obviously we see big problems with that", Sanders said.
He accused Iran of committing "multiple violations" and promised to work with Congress to "address the deal's many serious flaws".
On Thursday, hours before Mr. Trump made his decision, European foreign ministers met in Brussels with Iran's foreign minister, Mohammad Javad Zarif, ostensibly to press Tehran about its destabilizing activities in the region, which are putting the nuclear deal at risk.
He said there was a "strong consensus in Brussels today" that Iran was complying with the deal and that "any move that undermines (the agreement) is unacceptable". The Trump administration and congressional leaders have sought European agreement on ways to toughen the deal, and such agreement is considered essential before US legislation could go forward. "It is also necessary that our US allies do the same and should be seen doing the same", Le Drian said after meeting with his Iranian, British, German and French counterparts. "We do not hide the other points of disagreement that exist", Le Drian said.
These senior officials and congressmen do not actually oppose the JCPOA; they oppose it in its current form and claim to want to "fix" it.
"The decision meeting is this afternoon", he said.
Steve Goldstein, the State Department's under secretary of state for public diplomacy, said US responses to the Iranian protests should be kept separate from decision-making on USA participation in the deal.