'The Guardians Council has started a partial recount of 10 per cent of the ballot boxes,' state-owned Arabic-language television Al-Alam said.
The opposition is demanding a complete rerun of the vote and has staged massive demonstrations in a dispute that has shaken the very foundations of the Islamic regime.
On Sunday, riot police in Teheran dispersed about 3,000 supporters of Mr Ahmadinejad's strongest rival Mir Hussein Mousavi who defied a ban on public gatherings, witnesses said.
A witness spoke of a 'minor confrontation' between police and the demonstrators who had gathered around Ghoba mosque to mark the anniversary of a prominent cleric killed in a bombing 28 years ago.
The information could not be independently verified as foreign media are banned from the streets under tough new restrictions imposed by the authorities in the wake of the election.
The Guardians Council, an unelected body of 12 jurists and clerics, has set up a committee to conduct the recount but Mr Mousavi and fellow defeated candidate Mehdi Karroubi rejected the panel and declined to send any representatives to oversee the count.
Mr Karroubi, a reformist former parliament speaker, insisted in a letter to the council on Sunday that a partial recount was 'not enough' and called for an independent body to probe 'all aspects of the election'.
Mr Mousavi, who was prime minister in the post-revolution years, won 34 per cent of the vote against 63 per cent for Mr Ahmadinejad, a gap of 11 million votes, according to official results. Mr Karroubi came a distant fourth with less than one per cent.
The Paris-based International Federation for Human Rights said on Sunday that more than 2,000 people are still in detention and hundreds more are missing across Iran since a government crackdown on protesters and opposition supporters.
Since the election at least 17 people have been also killed and many more wounded in clashes with security forces, according to state media.
Among those arrested are reformists, journalists and analysts, including supporters of Mr Mousavi and even some figures closed to top officials, in a sign of cracks appearing within the regime over the election. -- AFP