GENEVA (AFP) - World powers and Iran have yet to reach a deal on Iran's nuclear programme but are working hard to do so, United States Secretary of State John Kerry said on Friday.

"There is not an agreement at this point," Mr Kerry told reporters shortly after arriving in Geneva on Friday to help seal what is hoped to be a landmark deal with Teheran.

Mr Kerry, who broke off a Middle East tour to join the ongoing negotiations in the Swiss city, stressed that "there are still some very important issues on the table that are unresolved".

"It is important for those to be properly, thoroughly addressed," he said, adding though that the six world powers leading the talks with Teheran were "working hard" to reach an agreement.

Mr Kerry's comments came on the second and last scheduled day of crunch international talks on Iran's disputed nuclear programme.

The hoped-for agreement - seen as a first step ahead of further talks on a final deal - could see Tehran freeze its nuclear efforts for as long as six months in exchange for some relief from the sanctions that have battered its economy.

In addition to Mr Kerry, the foreign ministers of France, Britain and Germany also arrived on Friday following last-minute announcements they would join the talks.

Iranian Foreign Minister Mohammad Javad Zarif also cancelled a trip to Rome to continue the talks.

The unexpected convening of some of the world's most high-ranking diplomats has sparked widespread hopes that a deal may be in sight.

But Mr Kerry, who is set to meet with his French counterpart Laurent Fabius and European Union foreign policy chief Catherine Ashton separately on Friday afternoon before a trilateral meeting including Mr Zarif, pointed to continued disagreements and tried to dampen expectations.

"We hope to try to narrow those differences but I don't think anybody should mistake that there are some important gaps that have to be closed," he said.