The decision, first reported by the Associated Press, keeps the United States in the Iran deal, at least for the time being, despite Trump's suggestion last year that he was inclined to walk away from it. Most of Trump's national security advisers, including Secretary of State Rex Tillerson and Defense Secretary Jim Mattis, have urged him to waive the sanctions again.
Had Trump decided to reimpose nuclear sanctions that the Obama administration suspended almost two years ago to the day, the United States would have reneged on its commitment under the deal and isolated itself from allies that have insisted they will stick with it.
It could also have emboldened Iranian hard-liners. The political unrest, which rocked the clerical and political establishment, spread amid deep disappointment that sanctions relief provided by the nuclear deal has not trickled down economically to ordinary Iranians. Some analysts say that the United States would be seen as turning its back on the protesters and their economic demands if it reimposes broad economic sanctions.
Instead, any additional sanctions imposed now or in coming weeks would probably target the government or military elite, and not the wider Iranian economy, two officials said.
A spokesman for the White House National Security Council did not respond to a request for comment.
On Wednesday night, press secretary Sarah Huckabee Sanders posted a statement on Twitter condemning arrests of Iranian protesters.
"We will not remain silent as the Iranian dictatorship represses the basic rights of its citizens and will hold Iran's leaders accountable for any violations," she wrote.
Refusing to waive sanctions would have empowered Iranian hard-liners who distrust the United States and turned Washington into an adversary they could blame for internal disruptions, said John Glaser, head of foreign policy studies at the libertarian Cato Institute.
"It would be insulting if the United States and its leaders would try to take credit for the protests or superimpose them onto our own political, domestic issues here," he said.
The president faces deadlines beginning Friday to approve the continued relief from sanctions, Iran's main benefit from the landmark 2015 agreement that Trump has called the "worst deal" imaginable for the United States. He also faces another deadline to tell Congress whether he will "certify" that Iran is complying with the deal and that it is serving the interest of the United States.
Trump withheld that certification at the last deadline, in October, and his anticipated decision to do the same this time would have no immediate effect. But he seems to be laying the groundwork for an eventual withdrawal.
Officials and observers interviewed this week said Trump has been advised against making big changes now, before Congress has come up with promised legislation to address concerns about what he calls loopholes in the deal and add conditions for future U.S. participation.
Officials and others who spoke on the condition of anonymity because the decisions are not final said they expect Trump to agree with that approach but cautioned that he could still balk. At issue is the Republican president's resentment at being asked to keep alive a deal he loathes, and that his Democratic predecessor considered a signature accomplishment.
Under current law, the president has to suspend nuclear sanctions on a rolling basis — each time the certification deadline or separate deadlines to keep the sanctions in suspension come due.
The congressional leaders working on what they call "fixes" to the deal met with White House national security adviser H.R. McMaster last Thursday to recommend that the president continue to suspend nuclear sanctions, congressional and administration officials said.
Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) and ranking Democrat Benjamin L. Cardin (Md.) have been working together on a package that would address Trump's concern that the deal only delays Iran's ability to obtain a nuclear weapon. Various members of Congress and U.S. allies, including Israel, have said that as restrictions against Tehran are lifted under the deal, Iran's "breakout" window will shorten dramatically.
The deal expanded the breakout window from an estimated two months before the negotiations to one year, presumably giving governments time to react if Iran were found to be cheating. But some of the current restrictions eventually expire.
Sen. Tom Cotton (R-Ark.), who has been an influential voice for Trump on Iran issues, has warned that by 2030 the breakout window will be "a matter of weeks."
Corker accompanied Trump to Nashville on Monday, riding with the president on Air Force One with the goal of making his case about holding the line.
Changing the terms of the agreement itself would require approval from European co-
signers as well as Russia, China and Iran.
Iran is a signatory to the Nuclear Non-Proliferation Treaty, committing itself to never pursue nuclear weapons, but it is entitled to use nuclear technology for peaceful purposes.
If Trump again withholds Iran's certification, much of the world may shrug it off.
"His so-called violations of spirit are outside the scope of accord, and Iran remains in compliance with its commitments," said Kelsey Davenport, who has researched Iran's nuclear and missile programs for the Arms Control Association. "So his posturing on the ineffectiveness of the deal and its weaknesses is expected. An immunity is built up in the international community."
European allies have repeatedly urged the United States not to walk away from the agreement and to deal separately with concerns about Iran's missiles, human rights abuses and support for militant groups in neighboring countries.
Mark Dubowitz, head of the nonpartisan Foundation for Defense of Democracies, said he expects more non-nuclear sanctions over some of the issues that protesters were most concerned about, including corruption, human rights abuses and "cyber repression."
"Are we actually going to see measures that strike a blow at the heart of the regime's corruption and repression, or are they going to be meaningless sanctions targeting a few individuals?" Dubowitz said. "I hope we're going to see them strike at the supreme leader's network of foundations and companies he has built on the back of illegally expropriated Iranian private property. It's a target-rich environment, if the administration is serious."