Iran and the US are set to start negotiations on Friday to de-escalate tensions that have threatened to spiral into war, with Tehran saying the talks will be the first stage of a longer diplomatic process.

Repairs at key missile sites began soon after they were hit by Israeli and U.S. strikes last year, but work at Iran’s nuclear facilities has been slower.

Differences over the scope for the talks have also cast doubts on whether it will still go ahead, keeping open the risk of U.S. military action.

Iran requested to move talks from Turkey, Secretary of State Rubio confirms. Rubio laid out what topics needed to be discussed for a "meaningful" result.

President Donald Trump said Wednesday that he and Chinese President Xi Jinping discussed the situation in Iran in a wide-ranging call as the U.S. administration pushes Beijing and others to further isolate Tehran.

Crucial talks between the US and Iran appear set to be held in Oman as Tehran seeks to ensure the scope of its negotiations with the Trump administration is limited solely to its nuclear programme.