Mohamed ElBaradei said the talks will continue on Wednesday morning
Talks between Iran and world powers on a uranium enrichment deal are making slower-than-expected progress, the head of the UN's nuclear watchdog has said.
Mohamed ElBaradei said "many technical issues" had to be analysed, but insisted they were "moving forward".
The negotiations were stalled for most of Tuesday after Iran said it did not want France to be part of the deal, but briefly resumed late in the evening.
Iran is considering a proposal to send uranium abroad for further enrichment.
This is seen as a way for Iran to get the fuel it needs, while giving guarantees to the West that it will not be used for nuclear weapons.
Tuesday's talks in Vienna - involving Iran and three of the five permanent members of the UN Security Council, as well as the International Atomic Energy Agency - faltered after the Iranians said they would curb enrichment, something seen by the Western powers as essential, and objected to France's involvement.
All sides eventually returned to the negotiating table for about an hour after the US and Iranian representatives met in Mr ElBaradei's office. Few details of the meetings were released.
Mr ElBaradei, director general of the IAEA, said the talks would resume at 1000 (0800 GMT) on Wednesday.
"I believe we are making progress. It is maybe slower than I expected. But we are moving forward," he told reporters.
He said the process was complex, and involved "many technical issues" as well as "confidence-building guarantees".
The Iranian ambassador to the IAEA, Ali Asghar Soltanieh, meanwhile said the consultations had been "constructive".
Earlier, Iran's Foreign Minister, Manouchehr Mottaki, objected to Paris being part of the enrichment deal because it had reneged on nuclear fuel contracts in the past.
"There is Russia, America... I believe these countries are enough," he said.
"France, based on its shortcomings to fulfil its obligations in the past, is not a trustworthy party to provide fuel for Iran."
Mr Mottaki also reiterated any agreement would not mean the suspension of Tehran's enrichment activities.
"Iran will continue its uranium enrichment. It is not linked to buying fuel from abroad," he said.
"The meetings with world powers, and their behaviour, shows that Iran's right to have peaceful nuclear technology has been accepted by them."
The proposed scheme hinges on an arrangement in principle that Western negotiators announced after talks in Geneva earlier this month.
Under it, Russia and France would treat most of Iran's low-enriched uranium and turn it into fuel rods for a research reactor in Tehran.
Diplomats say a compromise is being considered under which Iran would sign a contract with Russia, which would then sub-contract work to France.
Correspondents say the deal would see Iran get the fuel it needs, tacit acknowledgement of its right to enrich uranium, and no new sanctions.
The West would meanwhile get a guarantee that Iran's existing stockpile will not be diverted to make nuclear bombs, they add.
Last month, the revelation of a second uranium enrichment plant in Iran further raised Western fears that Iran was trying to develop nuclear weapons. A nuclear bomb requires highly enriched uranium.
The Iranian government has said it will allow IAEA inspectors into the site, thought to be near the holy city of Qom.