Iran has agreed to hold a fourth round of indirect nuclear talks with the United States on Sunday in Oman, the semi-official Tasnim News Agency has reported, citing a member of the Iranian team.

The fourth round of negotiations, initially scheduled for May 3 in Rome, was postponed, with mediator Oman citing "logistical reasons".

"Following a proposal by the Omani foreign minister to hold the fourth round of talks on Sunday, Tehran has announced its agreement," Tasnim quoted the unnamed member of Iran's delegation as saying. "The fourth round of Iran-US talks in Oman has been finalised."

US President Donald Trump, who withdrew the US from a 2015 nuclear deal between Iran and world powers, has threatened to bomb Iran if no agreement is reached with his administration to resolve the long-standing dispute.

Western countries say Iran's nuclear programme is geared toward producing weapons, whereas Iran insists it is purely for civilian purposes.