GENEVA — U.S. Secretary of State John Kerry and five foreign ministers joined Iran nuclear talks Saturday, cautioning there were no guarantees their participation would be enough to seal a deal to curb Tehran’s atomic program.

The goal is a six-month agreement to freeze Iran’s nuclear program while offering Iran incentives through limited sanctions relief. If the interim deal holds, the parties would negotiate final stage deals to ensure Iran does not build nuclear weapons.

But it was unclear whether the current round, which began Wednesday, would produce any first-stage deal.

Britain’s Foreign Secretary William Hague spoke of `’very difficult negotiations,” saying “narrow gaps” remain on the same issues that blocked agreement at the last round earlier this month.

“We’re not here because things are necessarily finished,” Hague told reporters. “We’re here because they’re difficult, and they remain difficult.”

Kerry and his counterparts from Russia, Britain, France, China and Germany headed for Geneva after diplomats said Friday that Iranian Foreign Minister Mohammad Javad Zarif and top European Union diplomat Catherine Ashton had made progress on a key sticking point — Iran’s claim to a right to produce nuclear fuel through uranium enrichment.

Details were not released but it appeared the two sides were trying to reconcile Iran’s insistence that it has a right to enrich for peaceful purposes while assuaging fears that Tehran was secretly trying to build a bomb, a charge the Iranians deny.