A fourth round of talks between the US and Iran over Tehran's nuclear programme have taken place in Oman, with both sides agreeing to meet again, BBC reported.

US Middle East Envoy Steve Witkoff said the discussions in Muscat were encouraging, while Iran's Foreign Minister Abbas Araghchi described them as "difficult but useful". 

The US has insisted that Iran must scrap its uranium enrichment to prevent the country developing nuclear weapons, but Tehran denies it has such an aim and on Sunday again stressed it did not intend to give up the programme.

Donald Trump pulled out of a previous nuclear agreement between Iran and five other world powers in 2018, according to BBC.