Iranian police say tip-offs from the public helped the force to arrest 40 people who took part in violent anti-government protests last month, an Iranian news agency reported on Tuesday.

In a bid to track down people involved in the protests on Ashura, the day of ritual Shi'ite mourning that fell on December 27, police have published pictures of scores of suspected rioters and asked the public to help identify them.

The move was a clear warning to the pro-reform opposition and a further sign of the hardline authorities' determination to put an end to demonstrations that have continued to rock the Islamic Republic since last year's disputed election.

"Following the publication of the pictures of the Ashura day rioters...more than 40 people from the riotous elements were identified and arrested with the public's cooperation," ILNA news agency quoted an informed police source as saying.

Opposition backers, who have seized on occasions marked in the Islamic revolutionary calendar to revive their protests despite a widening crackdown, plan to take to the streets again on February 11, when Iran marks the revolution's 31st anniversary.

Messages of new protests on that day have been circulated on the Internet, including Facebook and chat rooms.

The 40 arrests reported by the ILNA news agency on Tuesday followed the detentions of hundreds of people on Ashura itself, when the Islamic Republic saw its most serious violence since the aftermath of the election seven months ago.

Eight people were killed in clashes between security forces and supporters of opposition leader Mirhossein Mousavi during the December 27 protests.

On Monday, five people detained on Ashura went on trial in a Tehran court on charges that could be punishable by death.

The election, which reformist leaders said was rigged in favour of President Mahmoud Ahmadinejad, touched off the worst internal crisis in the Islamic state's three-decade history. The government denied opposition charges of vote fraud.

Thousands of people, including senior reformers, were detained after the poll for fomenting unrest. Most of them have since been freed, but more than 80 people have been jailed for up to 15 years and five have been sentenced to death.