Iranian president Rouhani says Trump cannot undermine nuclear deal

Trump, who has called the pact "the worst deal ever negotiated", is expected to decertify the deal as he faces the 15 October deadline, a senior US administration official has said, a step which could cause the agreement to unravel.

"In the nuclear negotiations and agreement we reached issues and benefits that are not reversible. No one can turn that back, not Mr. Trump or anyone else," Rouhani said at a ceremony at Tehran University marking the start of the university academic year, state media reported.

"Even if 10 other Trumps are created in the world, these are not reversible."

If Trump does not certify that Iran is complying with the deal the US Congress will have 60 days to decide whether to re-impose sanctions on Iran which were waived under the agreement.

UN inspectors have verified that Iran is complying with the terms of the deal.

"If America carries out any violations today, the whole world will condemn America. They will not condemn Iran," Rouhani said, according to state media.

"Then they will say why did you trust America and sign an agreement with them?"

While Trump and his supporters in Washington have opposed the deal, US Secretary of State Rex Tillerson has advised against its repeal.

Britain and other key European nations have also urged that the accord be allowed to continue.

Earlier this week, US Defence Secretary James Mattis said the United States should remain in the nuclear deal negotiated during former President Barack Obama administration.