President Donald Trump said that the US would start direct talks with Iran over its nuclear programme on Saturday, warning that the Islamic republic would be in "great danger" if the negotiations failed.

Tehran confirmed the discussions set to take place in Oman, but stressed they were "indirect" talks.

"As the country that unilaterally withdrew from the comprehensive agreement on the Iran nuclear issue and caused the current situation, the US should demonstrate political sincerity (and)... mutual respect," Chinese foreign ministry spokesman Lin Jian said Tuesday.

Washington should "participate in dialogue and consultation, and at the same time stop its wrong practice of using force to exert extreme pressure", Lin said.

"China will continue to maintain communication with all relevant parties, actively promote peace and dialogue and push for a diplomatic solution at an early date," he added.

Trump's stunning announcement came after Iran dismissed direct negotiations on a new deal to curb the country's nuclear programme, calling the idea pointless.

The US leader pulled out of the last deal in 2018, during his first presidency.

There has been widespread speculation that Israel, possibly with US help, might attack Iranian facilities if no new agreement is reached.