Hossein Moussavian, part of a moderate negotiating team that served until 2005, was arrested "for security reasons" at his house in Tehran on Monday, the state-run IRNA news agency reported, citing an unnamed source.

The semi-official Fars news agency, also quoting an unnamed source, said that the former nuclear negotiator "was arrested and detained for a series of links with foreigners and exchanging information with them."

The source said "Moussavian had probably exchanged information with foreigners over nuclear issues and he could face espionage charges."

Fars, which had earlier reported the arrest was linked to business dealings, said Moussavian was now being interrogated at Tehran's notorious Evin prison.

"As he is being interrogated, his release is ruled out for the moment," its source said.

The office of Moussavian, who also served as ambassador to Germany and now works for a research body, declined to comment on the report.

No named Iranian official has yet confirmed what charges Moussavian could face or even that he has actually been arrested.

Moussavian served under Iran's then top national security official Hassan Rowhani during the Khatami presidency up to 2005 as a nuclear negotiator and also the negotiating team's main spokesman.

He played a central role in talks that saw Iran strike a deal with Europe under which it suspended its controversial uranium enrichment activities, a halt which was reversed when President Mahmoud Ahmadinejad came to power.

The nuclear negotiating team under Khatami was considered close to the centrist cleric and former president Akbar Hashemi Rafsanjani, who was thrashed by Ahmadinejad in 2005 presidential elections.

After Ahmadinejad came to power, Rafsanjani loyalists like Rowhani were removed from the team and replaced with more hardline officials under the new national security chief Ali Larijani, a conservative ex-television boss.

Iran has refused to consider a new suspension of enrichment under Ahmadinejad's rule, prompting the UN Security Council to impose two sets of sanctions against the Islamic republic.

In a speech in the southern city of Kerman on Wednesday, Ahmadinejad reaffirmed Iran's defiant stance, saying that it would "not yield an inch on our nuclear rights."

"We will resist until the end against those who want to violate our rights and will cut the hand of aggressors," said the president.

Since leaving the negotiating team, Moussavian has kept a relatively low profile, rarely making comments on the nuclear programme in public.

However in December last year he warned against the threat of full UN economic sanctions being imposed against Iran over its nuclear programme and urged the government to pursue a policy of "flexibility, caution and patience."

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