Iranian security forces fired warning shots in Tehran yesterday and beat opposition protesters among thousands seeking to renew their challenge to the government six months after a disputed election, witnesses said.

The security forces fired shots into the air as they clashed with supporters of opposition leader Mirhossein Mousavi at a state rally marking the killing of three students under the former Shah, the reformist website Mowjcamp said.

"Security forces are beating demonstrators, men and women. Some of them are injured and bleeding," said one witness in Tehran's central Haft-e Tir square.

The June 12 presidential election, which secured President Mahmoud Ahmadinejad's re-election, sparked Iran's worst unrest since the Islamic revolution three decades ago and exposed deep divisions in the establishment. Authorities deny allegations of vote-rigging.

Journalists working for foreign media were told by officials not to leave their offices to cover stories from yesterday until tomorrow but witnesses told Reuters hundreds of riot police battled protesters in various Tehran squares to disperse them.

Authorities shut down the mobile phone network in central Tehran to stop opposition protesters from contacting each other, the reformist website Rah-e Sabz said.

The opposition, which mainly relies on websites or mobile phone text messages to reach supporters, held similar protests sparking clashes with police in September and November.

"I saw at least 10 people being arrested and taken to minibuses," said one witness, while another said police fired teargas at demonstrators in Vali-ye Asr Square.

"Security forces shot into the air to disperse demonstrators in the Enqelab square," the Mowjcamp website said, adding at least two women were among those arrested.