US Secretary of State John Kerry will address the UN Human Rights Council in Geneva next week, the UN said Wednesday, confirming he will be in Switzerland as new Iran nuclear talks kick off.

"We have just heard now ... that Secretary of State Kerry will also be here to address the council on Monday," council president Joachim Ruecker told reporters.

Kerry will participate in the opening of the council's main annual session in Geneva, which will coincide with a new round of negotiations in Switzerland over Iran's nuclear programme.

Iran's Foreign Minister Mohammad Javad Zarif will also take part in the council session, together with his Russian counterpart Sergei Lavrov, EU foreign policy chief Federica Mogherini and other dignitaries.

The so-called P5+1 group of Britain, China, France, Russia, the United States and Germany are trying to strike an accord with Iran that would prevent Tehran from developing a nuclear bomb.

The West would, in return, ease the punishing sanctions it imposed on Tehran over its nuclear programme, which Iran insists is purely civilian in nature.

Negotiators are scrambling to make headway ahead of a March 31 deadline for agreement on a political framework.

The full deal must be agreed by the end of June, -- a cut-off point that looms all the larger after two previous deadlines were missed.

Kerry told a Senate hearing Tuesday that world powers "had made inroads" since reaching an interim deal with Iran in November 2013.

"And we expect to know soon whether or not Iran is willing to put together an acceptable, verifiable plan," he said, adding bluntly: "I don't know yet."

Moscow's top negotiator Deputy Foreign Minister Sergei Ryabkov meanwhile said there was "a growing confidence that an agreement will be reached by the assigned (June 30) deadline."

And Mogherini said a deal was "at hand," telling the Chatham House think tank: "We cannot miss this opportunity."