The European Union is pushing to bring US President Joe Biden's administration back into the nuclear accord to limit Tehran's ambitions.

The United States will not take part directly in the discussions also involving China, Germany, Russia, and Britain.

But for the first time since former leader Donald Trump pulled out of the Iran agreement in 2018, a US delegation will be present.

The 2015 nuclear accord saw Iran granted relief from international sanctions in exchange for accepting limits on its programme aimed at easing fears it could acquire atomic weapons.

Biden has promised to rejoin the agreement on condition Iran first returns to respecting commitments it abandoned in retaliation for Trump pulling out and reimposing swingeing sanctions.

Le Drian spoke to Iranian counterpart Javad Zarif on Saturday and "welcomed the coming resumption in Vienna of discussions on the nuclear dossier".

He also "encouraged Iran to be constructive in the discussions ... to identify in the coming weeks what needs to be done for a full return to respecting the agreement," Le Drian said in a statement.

"France will take part in a pragmatic and at the same time demanding way.

"I called on Iran to refrain from any further violation of its current commitments in the nuclear field likely to damage the dynamics of a resumption of discussions," he added.

Tehran says Washington has to end sanctions before it will make any moves to get back in line and has refused to hold direct negotiations with the US.

US State Department spokesman Ned Price called the Vienna talks a "healthy step forward" and Washington "remains open" to a direct encounter with Tehran.