MOSCOW, July 29 (RIA Novosti) - Court trials will begin on Saturday for 20 demonstrators arrested during last month's post-election riots in Iran, the state-run IRNA news agency reported on Wednesday.

The announcement comes a day after Iran's authorities agreed to release around 140 prisoners detained in the riots, which followed the controversial re-election of President Mahmoud Ahmadinejad on June 12.

The protestors facing trial are accused of vandalizing public and private property, illegally possessing weapons including grenades, recruiting killers, attacking police, and providing video material and images to "enemy media," IRNA said.

Iranian authorities have come under increasing pressure over treatment of detainees arrested in the protests, amid opposition allegations that prisoners have suffered inhumane treatment including torture. Supreme leader Ayatollah Ali Khamenei earlier this week ordered the closure of a prison that "did not possess the required standards to ensure the rights of detainees."

Iran's political crisis has continued since the wave of post-election protests triggered by alleged vote rigging. Over 20 people were killed and about 1,000 arrested during the riots.

Regional media reports say some 200 people remain in jail, including 50 opposition activists. The national ban on opposition protests remains in force, and authorities have refused permission for a memorial service for the riot victims, which had been scheduled for Thursday.