The 2015 deal, known as the Joint Comprehensive Plan of Action, was signed by the US under the previous administration of president Barack Obama as well as Iran, China, Russia, Britain, France and Germany.
The top Chinese diplomat noted that the implementation of the accord had not been "derailed" but would face "some new complicating factors". The nuclear deal removed a number of sanctions on the Central Bank, and there had been reports that Trump would impose new sanctions, albeit not for reasons related to Iran's nuclear development. "I'm not sure when the announcement will be made, whether it will be made tonight or whether it will be tomorrow", he said.
Republican Senator Bob Corker said "significant progress" had been made on bipartisan congressional legislation to "address the flaws in the agreement without violating USA commitments".
The United States is the only party that has threatened to scrap the deal, a stance that has been confronted by other participants.
Iran says its nuclear programme has only peaceful aims and says it will stick to the accord as long as others respect it.
In return, decades of global and USA nuclear-related sanctions were suspended, and the United States president must sign a waiver suspending them every 120 days.But Mr Trump has repeatedly criticised the deal - reached under his predecessor Barack Obama - as "the worst ever".
Congress has so far shown little interest in using legislation to undercut or change the current Iran nuclear deal.
However, time after time, President Trump has (perhaps reluctantly) certified that Iran was cooperating with the deal. One US official told the Washington Times that the actions "will send a very strong message that the United States is not going to tolerate their continued abuses".
That decision came despite the United Nations having certified Iran's compliance with the deal eight times.
Trump had faced a Friday deadline to decide on whether to waive the sanctions.
Britain, France and Germany called on Trump on Thursday to uphold the pact.
Iran will definitely respond to the US act by putting the name of Ayatollah Sadeq Amoli Larijani on list of sanctions.
Rouhani had promised that the 2015 deal he struck with Obama and other world leaders would lead to economic improvement, but "Iranians have not seen as robust an economic recovery as many had expected", according to an October 2017 analysis by Zachary Laub of the Council on Foreign Relations. Trump has repeatedly criticized the accord, while Iran has accused the US of failing to comply with it. Broadly, the sanctions are meant to target Iran's "destabilizing behavior".