Iranian security forces have fired tear gas amid clashes with protesters in central Tehran, opposition members and reformist websites say.

The reported clashes came as the opposition called on people to take to the streets as the Shia Muslim festival of Ashura reached a climax.

There have been days of sporadic protests in various cities across Iran.

Hundreds of police and security forces were said to have been deployed in Tehran ahead of Sunday's protests.

Tensions have risen in Iran since influential dissident cleric Grand Ayatollah Hoseyn Ali Montazeri died a week ago aged 87.

Supporters of opposition leader Mir Hossein Mousavi have sought to use Shia religious festivals this weekend to show continued defiance of President Mahmoud Ahmadinejad's government.

Denied the right to protest, the opposition chose the highly significant festival of Ashura when millions of Iranians traditionally go onto the streets for ceremonies and parades, BBC Tehran correspondent Jon Leyne says.

The festival mourns the 7th Century death of Imam Hussein, a grandson of the Prophet Muhammad.
BBC News - Tehran police 'fire tear gas at opposition protesters'