Kerry and Zarif during previous meeting in Geneva
Kerry and Zarif during previous meeting in GenevaReuters

A day after warning that President Barack Obama would not extend nuclear talks with Iran again, Secretary of State John Kerry arrived in Geneva on Sunday for fresh talks with his Iranian counterpart on Tehran's nuclear program.

Kerry finally sat down with Iranian Foreign Minister Mohammad Javad Zarif on Sunday evening after being delayed for several hours in London, the AFP news agency reported.

The two men are expected to continue their discussions Monday.

"Tonight's meeting is another step in a long, tough process," a senior State Department official was quoted as having said.

U.S. and Iranian diplomats have been meeting in Geneva since Friday, and senior negotiators from the so-called P5+1 group of Britain, China, France, Russia, the United States and Germany also met with Iranian negotiators Sunday to help drive the talks forward.

There is a heightened sense of urgency as the clock ticks down towards a March 31 deadline to agree on a political framework for the deal.

Kerry warned in London Saturday that "there are still significant gaps, there is still a distance to travel."

But, he added, "President (Barack) Obama has no inclination whatsoever to extend these talks beyond the period that has been set out."

On Sunday, Akbar Velayati, the diplomatic adviser to Iran's supreme leader Ayatollah Ali Khamenei, shot back at Kerry’s remarks and said that "if American leaders don't want to negotiate, it's up to them, but they were the ones who were after negotiations."

Iran and the six world powers reached an interim deal in November of 2013, under which Iran committed to limit its uranium enrichment to five percent and is gradually winning access to $4.2 billion of its oil revenues frozen abroad and some other sanctions relief.

The sides were then supposed to continue talks and turn the interim deal into a permanent one. However, the talks have stalled and two deadlines for a final deal have been missed, with a third one looming on July 1. Under the new agreement, a political framework must be reached by March 31.

Recent reports indicated that the United States is ceding ground to Iran in talks and will now allow it to “keep much of its uranium-enriching technology,” thus allowing Iran to maintain its self-proclaimed “right to enrich uranium”.

Before the talks were extended until July, Iran was toughening its stance, with chief negotiator Abbas 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.