The United States and Iran opened high-stakes talks on Tehran's nuclear programme on Saturday, with President Donald Trump threatening military action if they fail to produce a deal.

The two sides entered "indirect" talks -- via an intermediary -- in the Omani capital Muscat, Iran's foreign ministry said. The Americans had called for the meetings to be face-to-face.

Disagreement over the format indicated the task facing the long-term adversaries, who are seeking a new nuclear deal after Trump pulled out of an earlier agreement during his first term in 2018.

Foreign Minister Abbas Araghchi was leading the Iranian delegation while Trump's special envoy Steve Witkoff headed the US team.

"Our intention is to reach a fair and honourable agreement from an equal position," Araghchi said in a video posted by Iranian state TV.

Iran, weakened by Israel's pummelling of its allies Hezbollah in Lebanon and Hamas in Gaza, is seeking relief from wide-ranging sanctions hobbling its economy.

Tehran has agreed to the meetings despite baulking at Trump's "maximum pressure" campaign of ramping up sanctions and repeated military threats.

Meanwhile the US, hand-in-glove with Iran's arch-enemy Israel, wants to stop Tehran from ever getting close to developing a nuclear bomb. (AFP)