US Secretary of State John Kerry insisted on Tuesday there was a "diplomatic path" to be forged with Iran on its disputed nuclear programme, as world powers and Tehran held crunch talks.

"There is a diplomatic path," said Kerry after meeting his German counterpart Guido Westerwelle in Berlin. He expressed his "hope" that "Iran itself will make its choice to move down the path of a diplomatic solution."

The five permanent UN Security Council members and Germany -- the so-called P5+1 -- are meeting the Iranian team headed by top nuclear negotiator Saeed Jalili in Kazakhstan in a bid to break the deadlock over Iran's programme.

Kerry said it "would really be a mistake in the middle of the talks for me to try to talk at any length about what the dynamics of those talks are."

"I want these talks to have their chance to work through before I comment," added the secretary.

Nevertheless, he urged Tehran to accept the offer of western powers, saying they included "reciprocal measures that encourage Iran to make concrete steps in order to begin addressing the international community's concerns."

The world powers are offering Iran permission to resume its gold and precious metals trade as well as some international banking activity which are currently under sanctions, Western officials told AFP.

But in exchange, Iran will have to limit sensitive uranium enrichment operations that the world powers fear could be used to make a nuclear bomb, the sources added.

The two-day meeting in the Kazakh city of Almaty comes as sanctions bite against the Islamic republic and Israel still refuses to rule out air strikes to knock out Iran's suspected nuclear weapons drive.

Westerwelle for his part said the talks were "an opportunity that I really hope the Iranians will take."

"Our goal is a diplomatic solution in the nuclear argument with Iran but there must be substantial progress because a nuclear-armed Iran is unacceptable to us," added the minister.

"It would endanger not only the region but it would be a danger for the security architecture of the whole world."