Tehran (AFP) - Iran protesters have attacked a religious school in Karaj province near Tehran, the conservative Fars news agency reported on Saturday.

"At 9 pm (1530 GMT on Friday) they attacked the school and tried to break the doors down and burn things," Fars quoted the head of the school in the town of Ishtehad, Hojatoleslam Hindiani, as saying.

It gave only his clerical rank -- Hojatoleslam -- not his given name.

"They were about 500 people and they chanted against the system but they were dispersed by the riot police and some have been arrested," Hindiani said.

Iranian authorities have barely mentioned days of protests in the cities of Isfahan, Shiraz, Mashhad and Tehran, driven by concerns over the economy as well as wider anger at the political system.

During past unrest, conservative outlets have focused on attacks against sensitive symbols such as religious buildings as a way of tarnishing the protests.

Videos on social media in recent days have shown people chanting "Death to the dictator", but these have been impossible to verify and the authorities have charged that they are promoted by emigre opposition groups funded by the US, Israel and Saudi Arabia.

Describing the attack on Friday evening, Hindiani said: "These people came with rocks and broke the sign and all the windows of the prayer house and they were chanting against the system."

Foreign media are barred from observing or filming "unauthorised" protests.

The videos on social media suggest protests in recent days are far from the scale of the unrest seen in December and January, when at least 25 people were killed in demonstrations that spread to dozens of towns and cities.