Tehran, July 17 (DPA) Former Iranian president Akbar Hashemi-Rafsanjani called Friday for an 'open debate' on the recent controversial election which saw President Mahmoud Ahmadinejad retain power as witnesses said 'hundreds of thousands' of people surged to hear him.

He also called on authorities in a Friday prayers address to release opposition figures who have been imprisoned during a major crackdown on protesters which followed the election June 12.

Rafsanjani, who still enjoys major influence in Iran, was addressing opposition supporters amid tight security, high anticipation and tension outside Tehran University.

Witnesses said 'hundreds of thousands' of opposition supporters had gone to the central Tehran venue, but only thousands reached the front gate of the Tehran university.

A radius of more than three kilometres was filled with people surging towards the university, witnesses said. Most were unable to get anywhere near the prayer venue, where large numbers of police and volunteer security forces formed a tight security cordon.

Rafsanjani began the speech with an appeal for calm. 'Let us use the occasion to create a better future for our country,' he told the crowd in his first public appearance since the election.

He urged them not to disrupt the peaceful Friday prayers atmosphere with anti-government chants, witnesses said.