The EU's top diplomat Catherine Ashton will meet chief Iranian nuclear negotiator Saeed Jalili in Istanbul on May 15 in a fresh effort to defuse international concern over Tehran's disputed nuclear drive.

Ashton's office said "the talks are a follow-up to the last round of negotiations held in Almaty" on April 5 and 6 that failed to produce an accord.

The EU foreign policy chief represents the five permanent UN security council members -- Britain, China, France, Russia and the United States -- plus Germany in the so-called P5+1 talks aimed at reaching a deal on Iran's nuclear programme.

Ashton said after two days of talks in the Kazakh city that the positions were still "far apart".

World powers had offered some easing of the sanctions that have hurt Iran's economy in the past two years, in return for Tehran accepting limits on its nuclear programme.

But Ashton said after that the world powers were still waiting to see "real engagement" from Iran over the proposal.

Iran insists on international recognition of what it says is its "right" to enrich uranium, a key component of the nuclear fuel cycle which can also be used to make the explosive core of an atomic bomb.

But the world powers insist on Tehran ending enrichment to high levels and verifiably suspending operations at the Fordo mountain bunker where such activity takes place before recognising Iran's rights to less threatening nuclear activities.

Iran has reportedly been offered the right to deal in some precious metals and perform small financial transactions now prohibited by the international sanctions. Tehran says it is being asked too much for too little in return.

The P5+1 grouping is especially worried about Iran's enrichment to levels of up to 20 percent and wants the Islamic republic to ship out the part of its 20-percent enriched uranium not converted into powder for reactor fuel.

Iran denies it is developing the atomic bomb and argues that it requires a nuclear programme solely for peaceful medical and energy needs.