A reformist former government spokesman detained after Iran's disputed election in June has been sentenced to six years in jail, the semi-official Fars news agency reported on Thursday.

It said Abdullah Ramezanzadeh, who backed opposition leader Mirhossein Mousavi in the vote, was sentenced by a court on charges including acting against national security, propaganda against the Islamic system and possessing classified documents.

The report of his jail sentence coincides with mounting tension in Iran after the death of a leading dissident ayatollah and opposition reports of clashes between the cleric's supporters and security forces in the city of Isfahan on Wednesday.

Ramezanzadeh, who held his post during the 1997-2005 presidency of reformer Mohammad Khatami, was among scores of senior pro-reform figures and activists detained after the poll on accusations of fomenting post-election unrest.

'Based on the court's decision Ramezanzadeh was given a six-year obligatory jail sentence,' Fars quoted a Revolutionary court statement as saying. It did not say when the verdict was issued. Revolutionary courts usually handle security cases.

Last month, Iranian media said reformist former vice president Mohammad Ali Abtahi was also sentenced to six years in jail. He was later released on bail of $700,000 pending appeal.

Abtahi, one of dozens of leading moderates detained after the disputed election on charges of trying to topple the clerical establishment by orchestrating protests, was the most senior reformer to be jailed after the presidential election.

Thousands of people were arrested after the poll, which the opposition says was rigged in President Mahmoud Ahmadinejad's favour. Most of them have since been freed, but more than 80 have received jail sentences of up to 15 years in connection with protests and violence after the vote, the judiciary says.

The authorities reject the opposition's vote rigging charges and have portrayed the huge opposition protests that erupted after the election as foreign-backed.

Some hardliners have called for legal action against Mousavi, who came second in the election and has vowed to press on with his drive for political reform in Iran. Any such move may trigger new street protests by his backers.

Despite arrests and crackdowns, opposition supporters have continued to stage sporadic rallies over the last six months.

Tension has increased again after Saturday's death of Iran's leading dissident cleric, Grand Ayatollah Hossein Ali Montazeri, in the holy city of Qom at the age of 87.

His death occurred in the tense run-up to Ashura on December 27, a politically important Shi'ite religious commemoration that offers the opposition another opportunity to show its strength. – Reuters