Kerry and Zarif before a meeting in Geneva
Kerry and Zarif before a meeting in GenevaReuters

U.S. Secretary of State John Kerry and Iran's foreign minister, Mohammad Javad Zarif, held intensive talks on Tehran's disputed nuclear program on Wednesday, returning for an evening session before handing off to their deputies, officials told Reuters.

Kerry and Zarif "had substantive meetings for approximately five hours today and they discussed a broad range of issues with a small group of staff from each side," a senior State Department official was quoted as having said.

But Kerry later unexpectedly returned to the Geneva lakeside hotel for a third meeting lasting some 90 minutes with Zarif after briefing senior negotiators ahead of their technical-level talks scheduled with Iranian counterparts for Thursday in the Swiss city.

"Secretary Kerry and Foreign Minister Zarif reconvened this evening to continue discussion about the nuclear negotiations in advance of the start of the next round of talks tomorrow," a State Department spokeswoman said, according to Reuters.

Wendy Sherman, acting deputy secretary of state, and deputy foreign minister Abbas Araqchi are to lead their delegations at Thursday's talks, to be followed on Sunday January 18 by wider talks between Iran and major world powers.

Earlier, Zarif said that serious dialogue with the West would be easier if it respected Muslim sensitivities, ruffled by the latest Charlie Hebdo cartoons.

Speaking to reporters before talks began, Zarif said the meeting would help gauge whether both sides were ready to advance toward a deal to curb Iran's nuclear program in exchange for sanctions relief.

"I think it's important. I think it will show the readiness of the two parties to move forward and to speed up the process," Zarif told reporters.

Tehran and the so-called P5+1 group of nations have been locked in talks since February on a permanent nuclear deal aimed at ending a decade-long diplomatic crisis.

Despite making progress, the two sides failed to clinch a definitive deal by a November deadline and agreed to extend the talks for another seven months.

Another inconclusive round of negotiations was held in Geneva between Iranian officials and the six powers in December. Araqchi said following those talks that they had been "very useful and helpful".

Diplomats fear that time may be running out, after two earlier deadlines for an accord were missed.

Before the talks were extended, Iran had been toughening its stance, with Araqchi saying he sees no prospect for a deal unless the other side abandons its “illogical excessive demands”.

A senior Iranian official followed those comments by declaring that Iran will demand that all Western sanctions be lifted as part of a final deal, rejecting an American proposal of a gradual lifting of sanctions.