United Nations nuclear inspectors and Iranian officials held what both sides described as "good" talks in Iran about suspicions that the Islamic Republic was seeking to develop atomic weapons, but said more discussions would be needed.
The UN inspectors went to Tehran on Saturday to confer with Iranian officials on Iran's suspected atomic weapons programme, and to try to advance efforts to resolve the nuclear row. Tehran says its nuclear activities are for peaceful electricity generation.
"We are committed to resolve all the outstanding issues and the Iranians said they are committed too. But of course there is still a lot of work to be done and so we have planned another trip in the very near future," Herman Nackaerts, deputy director general of the International Atomic Energy Agency, told reporters after returning from Tehran on Wednesday.
Asked if he was satisfied with the talks, Nackaerts, who headed the six-member IAEA mission, said: "Yeah, we had a good trip."
He described the three days of talks as "intensive discussions" but declined to comment on whether his Iranian counterparts had engaged in substantial dialogue or to give any more details, saying he first needed to brief his superiors.
Iranian Foreign Minister Ali Akbar Salehi also said more talks would be needed but did not say when.
"We had very good meetings and we planned to continue these negotiations ... the team had some questions about the claimed studies ... one step has been taken forward," he told the semi- official Fars news agency in Tehran on Wednesday.
"We were ready to show them our nuclear facilities, but they didn't ask for it."
Iran's chief nuclear negotiator, Saeed Jalili, had already announced Iran's readiness to hold talks with major world powers and would issue a written invitation, Salehi added.
"I hope this meeting takes place in the not too distant future," he said.
Western diplomats have often accused Iran of using offers of dialogue as a stalling tactic while it presses ahead with its nuclear programme, and say they doubt whether Tehran will show the kind of concrete cooperation the IAEA wants.
Tension between Iran and the West has increased sharply this year after Washington and the European Union imposed the toughest sanctions yet in a drive to force Tehran to provide more information on its nuclear programme.
The measures take direct aim at the ability of OPEC's second-biggest oil exporter to sell its crude.
Iran rejected the EU sanctions as "psychological warfare" and threatened to cut off oil exports to European countries before July 1 when the sanctions would be fully enforced.
Iranian officials have shrugged off the impact of sanctions, saying their country has become more self-reliant.