Iran's chief negotiator has said talks in Geneva with world powers through the night on implementing a nuclear deal had made "good progress".
Negotiations continued throughout the night until early on Tuesday morning in the Swiss city "and the two sides have made good progress on different issues", Abbas Araqchi, Iran's lead negotiator, said in comments carried by official news agency IRNA.
They are "going to submit their conclusions to the vice-ministers and political heads because there are still questions to be resolved on the political level," he said, stressing that "the experts had done their work".
He said there would probably be "a meeting next week with Olga Schmitt", the deputy to European Union foreign policy head Catherine Ashton, who has been representing the P5+1 group in Tehran.
Experts from Iran and the so-called P5+1, the US, Britain, France, Russia and China plus Germany, have been holding technical talks on implementing an agreement reached on November 24 on Iran's controversial nuclear programme.
The interim deal requires that Iran freeze or curb its nuclear activities for six months in exchange for some sanctions relief while the two sides try to reach a comprehensive agreement.
Hamid Baeedinejad, who heads the Iranian delegation of experts, said the Geneva agreement should be implemented in late January, the ISNA news agency has reported.
"According to the conclusions of talks held with technical experts from the P5+1 group, it has been agreed to start the application of he Geneva agreement in the last 10 days of January," he said.
Baeedinejad said that "political officials" from the two parties had yet to endorse an application date.
Tuesday's developments came as local media in Iran reported that a former nuclear negotiator close to President Hassan Rouhani who was sentenced to two years in prison in 2008 for actions against "national security", had returned to Iran.
"I have returned to Iran to stay," Hossein Moussavian said on Monday at the funeral for the mother of Mohammad Javad Zarif, foreign minister, according to the IRNA news agency.
He had been living in the US in recent years.
He had initially been accused of espionage and contacts with foreign embassies, but the charges were later dropped, leading Mahmoud Ahmadinejad, the former president, to demand that the "minutes of the discussions between Mr Moussavian and foreign diplomats be made public".