TEHRAN (AFP) - A former nuclear negotiator close to President Hassan Rouhani who was sentenced to two years in prison in 2008 for actions against "national security" has returned to Iran, media reported Tuesday.

"I have returned to Iran to stay," Hossein Moussavian told reporters on Monday at the funeral for the mother of Foreign Minister Mohammad Javad Zarif, according to the IRNA news agency. He had been living in the United States in recent years.

Moussavian was the spokesman for Iran's negotiating team when it was headed by Rouhani from 2003-2005.

But in April 2008, during the rule of hardline president Mahmoud Ahmadinejad, he was given a suspended two-year sentence and banned from public office for five years after the national security conviction.

He was briefly imprisoned in 2007 after being prosecuted on charges of collaborating with the British embassy.

He had initially been accused of espionage and contacts with foreign embassies, but the charges were later dropped, leading Ahmadinejad to demand that the "minutes of the discussions between Mr Moussavian and foreign diplomats be made public".

Moussavian has for the past few years lived in the United States, where he has regularly given interviews calling for an agreement with world powers on Iran's disputed nuclear programme.

Iran reached a landmark deal with world powers on Nov 24 that requires it to 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.

On Tuesday, Tehran's lead negotiator Abbas Araqchi said experts meeting in Geneva to discuss the implementation of the accord had made "good progress" in talks that ran until 4.30am (11.30am, Singapore time).

Western nations and Israel have long suspected Iran is covertly pursuing a nuclear weapons capability alongside its civilian programme, charges denied by Tehran, which insists its uranium enrichment is for purely peaceful purposes.