Hossein Moussavian, a close ally of ex-president Akbar Hashemi Rafsanjani, was freed after paying bail of 2 billion rials (215,000 dollars) at around 1:00 pm (0930 GMT), Iranian media reported.
"A two billion rial bail was issued for the release of Moussavian today, Wednesday, and the suspect was released," said Hassan Hadad, the Tehran deputy prosecutor in charge of security issues, according to the ISNA agency.
Moussavian, the spokesman of a moderate negotiating team that served under reformist president Mohammad Khatami to 2005, was arrested on April 30. He also served as ambassador to Germany under Rafsanjani.
Since leaving office, Moussavian has issued veiled criticism of President Mahmoud Ahmadinejad’s confrontational stance on the nuclear issue and called on Tehran to behave with pragmatism and flexibility in the standoff.
Sources indicated to the semi-official Fars news agency that investigations would continue into Moussavian’s case after his release.
"He has expressed sorrow and remorse over his deeds," said the Fars source. "The initial investigation is now completed and the subsequent investigation will be done by summoning him to the prosecutors’ office in person."
It said the Moussavian’s accusations "are not related to today or yesterday but have to do with (actions) many years ago" adding that the investigation had so far only foucussed on security issues.
Intelligence Minister Gholam Hossein Mohseni Ejeie said late on Tuesday that two other unnamed individuals had been summoned for questioning by intelligence agents in connection with the case.
Fars’ source said that one of the individuals — both of whom worked for security bodies — had been released on bail. It did not give details over the fate of the other suspect.
Fars has reported Moussavian was charged with spying on Iran’s controversial atomic programme but no officials have gone on the record to confirm this.
Government spokesman Gholam Hossein Elham denied that the arrest of Moussavian targeted as a group the moderate officials who handled the Iranian nuclear case until Ahmadinejad’s election.
"The issue is not specifically related to the nuclear people. The nuclear issue is not the only focus. Moussavian’s case is specifically linked to him as an individual," he told reporters.
Ahmadinejad replaced the entire nuclear negotiating team after thrashing Rafsanjani in the 2005 presidential elections and accelerated uranium enrichment activities, which had been suspended under a deal with Europe.
Moussavian is now deputy head of an international affairs research institute belonging to the Expediency Council, Iran’s top political arbitration body which is headed by Rafsanjani himself.
The head of the Strategic Studies Centre is Hassan Rowhani, a moderate cleric who until 2005 was Iran’s top nuclear negotiator and national security chief under Khatami.
Rafsanjani broke his silence on the affair more than a week after news of the arrest broke.
"The truth will be revealed soon," the Etemad newspaper quoted him as saying before asking reporters to allow him not to comment any further.