The son of one of Iran's founding revolutionaries was sentenced to several years in jail Sunday after releasing a decades-old tape in which his father denounced the mass execution of prisoners, local media reported.

Ahmad Montazeri, 60, was convicted by a clerical court in the holy city of Qom on charges of “acting against the national security” and “releasing a classified audio file”, the ISNA news agency reported.

He received a further year for “propaganda against the system”, ISNA said.

The court said he would only serve six years in view of his lack of previous convictions, his age, and “reverence” for a brother he lost in an insurgent attack.

Montazeri is the son of Ayatollah Hossein Ali Montazeri, who for decades was right-hand man to Ayatollah Ruhollah Khomeini, the father of Iran's Islamic revolution.

The elder Montazeri was one of the few Iranian leaders to voice opposition in 1988 when Khomeini ordered the execution of thousands of political dissidents held in the country's jails.

The order was directed primarily against the People's Mujahideen of Iran (MEK), an insurgent group that had sided with Saddam Hussein's Iraq in the eight-year war between the two countries.

Montazeri, who had been Khomeini's chosen successor, opposed the move despite the fact he had lost one of his sons to an attack by the MEK in 1981.

That opposition would lead to him being stripped of his status as deputy supreme leader, and he became a vocal critic of hardliners in the regime until his death in 2009.

In August Ahmad Montazeri released a 40-minute recording of his father from 1988, arguing with leading members of the judiciary about the executions.

Shortly after its release, Justice Minister Mostafa Pourmohammadi, who was one of the people allegedly featured on the tape, said he had no regrets about the executions.

“We are proud to have carried out God's commandment with regard to the (MEK) and to have stood with strength and fought against the enemies of God and the people,” Pourmohammadi said, according to the Tasnim news agency.

There is disagreement over the number of people executed in 1988, though Amnesty International has put the figure at around 5,000.