"We had fruitful talks with Lady Ashton last night," Saeed Jalili told a news conference in Istanbul a day after talks with Ashton, who is representing the P5+1 -- the United States, China, Russia, France, Britain and Germany.

"We hope our talks last night will contribute to an ongoing process for better understanding," he said.

Tuesday's meeting on the long-running row over Iran's contested nuclear drive, held behind closed doors at the Iranian consulate in Istanbul, marked the first direct talks since June.

In Brussels, Ashton's office said she aimed to meet with world powers in the coming days "in order to assess the situation and to discuss the way forward".

The foreign ministers of the P5+1 are due in New York for the UN General Assembly going into a "ministerial week" due to begin formally on September 24 and Ashton plans to meet them in a bid to get stop-start international diplomacy over Tehran's atomic programme moving again.

Jalili said Tehran would wait for the results of the P5+1 evaluation after their meeting with Ashton.

Turkey has twice been the venue of meetings on the nuclear standoff since the last negotiation process started earlier this year, with a major meeting held in April and a lower-level gathering in late July.

The P5+1 and Iran made no breakthroughs in the last round of talks in Moscow in June.

World powers have asked Iran to immediately stop enriching uranium because of fears Tehran might be developing nuclear weapons, and imposed a number of sets of sanctions.

But Iran rejects the allegations, saying its nuclear programme is peaceful, designed for energy and development purposes only.

European Union foreign affairs chief Catherine Ashton aims to meet with world powers in the coming days "in order to assess the situation and to discuss the way forward," her office said after the first direct talks since June on Tuesday night.

The foreign ministers of Britain, China, France, Russia, the United States and Germany are due in New York for the United Nations General Assembly going into a "ministerial week" due to begin formally on September 24.

Ashton plans to meet these key figures in the margins of the UN talks, in a bid to get stop-start international diplomacy over Tehran's contested atomic programme back moving.

No statements were made to the press at the beginning of Tuesday's meeting with Iran's top nuclear negotiator Jalili, which was held behind closed doors at the Iranian consulate in the Turkish city of Istanbul, starting at around 1930 GMT Tuesday.

Described simply as part of ongoing efforts "to seek a diplomatic solution," the talks followed negotiations in Moscow in June, a meeting of the respective heads' deputies in July and phone calls made over the summer, Ashton's statement said.

"While it was not a formal negotiating round it was a useful and constructive meeting and an important opportunity to stress once again to Iran the urgent need to make progress," said the declaration issued by EU High Representative Ashton's spokesman Michael Mann.

World powers have asked Iran to immediately stop enriching uranium because of fears Tehran might be developing nuclear weapons.

But Iran rejects the allegations, saying its nuclear programme is peaceful, designed for energy and development purposes only.

Jalili met earlier Tuesday with Turkey's Foreign Minister Ahmet Davutoglu to discuss the resumption of international talks over Tehran's atomic programme, a diplomatic source said.