US President Donald Trump has said it is highly unlikely he will order fresh attacks on Iran as long as negotiations over Tehran's nuclear programme and the reopening of the Strait of Hormuz show progress. Speaking to CNN in a 20-minute phone interview on Sunday, he repeated the phrase five times.

"It depends on whether or not they sign a very strong agreement," Trump told CNN's Jim Sciutto. "The answer is highly unlikely it's going to be necessary." He added that he would order strikes if necessary, saying the United States had already hit Iran hard and "could finish them off".

Trump said Iran was struggling financially and claimed the country had seen 301 per cent inflation this year, a figure he offered without evidence. He also claimed Iran now retained only 10 per cent of its missile capacity and 15 per cent of its drone capabilities, and said three US aircraft carriers in the region were "fully locked and loaded".

The president said US forces had identified potential targets inside Iran, including 38 bridges he claimed could be destroyed within an hour. Reuters, reporting CNN's account of the interview, confirmed those remarks.

The comments come eight months after the United States and Israel began attacks on Iran in February, with the two sides since locked in a stalemate and little diplomatic progress made. Qatar, which has mediated the talks, said on Friday that Trump had telephoned Emir Sheikh Tamim bin Hamad Al Thani to discuss de-escalation, and Iran's Foreign Minister Abbas Araghchi has spoken in recent days with counterparts from Saudi Arabia, the United Arab Emirates, Oman, Pakistan, Kuwait, Jordan, Turkey, Cyprus and Qatar.

Reuters reported on Thursday that Iran had submitted a nuclear proposal to Washington through Qatar, which the US was reviewing. A senior Iranian official told the agency that further discussion would depend on Washington first meeting Tehran's seven demands, including sanctions relief, access to frozen assets and war reparations, while Washington insists nuclear issues must feature in initial talks. Qatar said on Saturday that reports the two sides had failed to reach a deal were untrue and that both were continuing to work towards an agreement.