Iranian President Hassan Rouhani warned US President Donald Trump on Tuesday to stay in the nuclear deal Tehran signed with world powers in 2015, or face "severe consequences", as other signatories stepped up efforts to save the agreement.

Trump has said that unless European allies fix what he has called "terrible flaws" in the deal by May 12, he will restore US economic sanctions on Iran, which would be a severe blow to the pact.

The other powers that signed the deal - Russia, China, Germany, Britain and France - have all said they want to preserve the agreement that curbed Iran's nuclear programme in return for lifting most sanctions.

"I am telling those in the White House that if they do not live up to their commitments, the Iranian government will firmly react," Rouhani said in a speech broadcast live on state television.

"If anyone betrays the deal, they should know that they would face severe consequences," he told a cheering crowd of thousands gathered in the city of Tabriz. "Iran is prepared for all possible situations," he added.

French President Emmanuel Macron is in Washington, trying to convince Trump not to tear up the accord.

Russian Foreign Minister Sergei Lavrov said on Monday he had agreed with his Chinese counterpart that Moscow and Beijing would try to block any US attempt to sabotage the nuclear deal.

Iran has warned that it will ramp up its nuclear programme if the deal collapses.