World powers failed to make progress with Iran in two days of talks on its nuclear program, with the EU calling the discussions disappointing and saying no further meetings between the two sides were planned.

'This is not the conclusion I'd hoped for,' said European Union foreign policy chief Catherine Ashton at the end of the talks in Istanbul on Saturday.

'We'd hoped to embark on a discussion of practical ways forward and have made every effort to make that happen,' she added. 'I am disappointed.'

A senior US official who attended the talks and declined to be named also described the meeting as disappointing and said 'serious differences remained' between the two sides.

An aide to Iran's chief negotiator Saeed Jalili told Reuters that the talks would resume, even if the timing and venue were still undecided. However, Ashton said further talks depended on a more constructive approach from Tehran.

'The process can go forward if Iran chooses to respond positively,' she said. 'The door remains open. The choice remains in Iran's hands.'

The West suspects Iran wants to develop nuclear weapons while Tehran says its atomic energy program is peaceful.

The standoff has dragged on for eight years and expectations were low heading into the Istanbul talks between Iran and the six powers - the US, France, Germany, China, Russia and Britain - whose delegations were led by Ashton.

The talks were a follow-up to a meeting in Geneva last month which was the first set of discussions between the two sides in more than a year.

Their failure suggests that tougher sanctions against Iran, a major oil producer, have had little effect in persuading the Islamic state to cooperate more, though analysts say punitive measures are hurting the Iranian economy.

Earlier this week, US Secretary of State Hillary Clinton told US network ABC that the Obama administration may propose new unilateral steps against Iran.

Asked about the possibility of more sanctions, Ashton said it had not been part of the discussions in Istanbul, but pointed to the West's 'twin track' approach of applying pressure to keep the dialogue moving.

At the outset of the Istanbul meeting Iran insisted on preconditions that were unacceptable to the West, including the lifting of sanctions and recognition of its right to enrich uranium.

Jalili said after the talks ended that any agreement would have to be based on Iran's right to pursue enrichment.-Reuters