Iran resumed Tuesday the mass trial of opposition activists and protesters charged with rioting and plotting to topple the ruling Islamic system through a "velvet revolution" following the country''s disputed presidential election.

The proceedings in Tehran''s Revolutionary Court are seen as an attempt by the authorities to deliver a final blow to the pro-reform movement and discredit the anti-government protests that have persisted since the June 12 vote.

Hundreds of protesters, opposition politicians and activists have been arrested in the crackdown on the opposition, which has denounced President Mahmoud Ahmadinejad''s proclaimed election victory.

Tuesday''s hearing was the fourth so far in the extraordinary trial that started last month.

Iran''s official IRNA news agency said there were new defendants in the courtroom on Tuesday. They included former Deputy Interior Minister Mostafa Tajzadeh, former Deputy Foreign Minister Mohsen Aminzadeh and former government spokesman Abdollah Ramezanzadeh — all prominent reformists.