Hossein Moussavian, initially charged with "nuclear espionage", was given a two-year suspended prison term and banned from holding posts in diplomacy or foreign policy in the next five years.

"One of Moussavian's main heart arteries has been severely blocked by 60 percent and another heart artery by 40 percent," his lawyer Houshang Pour Babaie was quoted as saying.

"Therefore he is under serious medical supervision," he added.

Doctors have banned visitors, the lawyer said.

Moussavian was a leading nuclear negotiator in the moderate team that agreed a temporary suspension of sensitive nuclear activities with EU countries during the presidency of reformist Mohammad Khatami.

He was briefly detained and then released on bail in May 2007. The Iranian judiciary then cleared him of espionage charges in November of that year, infuriating the government which wanted to see him stand trial.

President Mahmoud Ahmadinejad had openly accused Moussavian of being a spy, with his intelligence minister, Gholam Hossein Mosehni Ejeie, claiming he supplied nuclear secrets to the British embassy in Tehran.

Moussavian has been acquitted of espionage charges and issued with a legal document confirming that the investigation against him had been concluded.

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