Riot police used tear gas and batons to break up a demonstration in Tehran on Thursday and clashed with mourners at a defiant graveside commemoration for people killed in election violence, witnesses said.
It was the first major violence between security forces and demonstrators in three weeks in Iran, where tensions are still running high over President Mahmoud Ahmadinejad's disputed re-election in June.
Police moved in as crowds massed around a major open-air prayer venue in central Tehran and a major thoroughfare nearby, defying a ban on a planned opposition memorial ceremony, witnesses said.
They used tear gas and batons against thousands of protesters on Vali Asr Street who were shouting "Death to the dictator!", "Free the political prisoners!" and slogans in support of opposition leader Mir Hossein Mousavi, they said.
Late into the evening, hundreds of riot police and Islamist vigilantes rode motorcycles around several streets in Tehran, to prevent people from gathering, they added.
Witnesses also reported clashes earlier at the Behesht-e Zahra cemetery south of Tehran, where hundreds of police with batons and belts beat some members of an estimated 2,000-strong crowd who hurled stones at security forces.
The US State Department described the use of force as "disturbing" and expressed solidarity with the right of Iranians to demonstrate.
"I think it's particularly disturbing to see security forces use force to break up a graveside demonstration," said State Department spokesman Ian Kelly.
Iranians were marking the 40th day since the death of Neda Agha-Soltan, a young woman who came to symbolise the public uprising over Ahmadinejad's June 12 victory which the opposition says was rigged.
A graphic Internet video of Neda bleeding to death was seen around the world and triggered an outcry over the sometimes brutal crackdown on demonstrators.
Some Iranian hardliners claim Neda's killing was "staged" to denigrate the regime and they seek to divert the blame from Islamist vigilantes cracking down on protesters.
"Today is a mourning day. Loyal Iranians are the mourners today," crowds shouted at the cemetery where Neda's grave was decorated with candles and flowers.
Police arrested several mourners, including prominent film director Jafar Panahi and his family, a witness said.
They also forced Mousavi out of the graveyard minutes after his arrival and although police initially surrounded fellow campaigner Mehdi Karroubi, he was able to give graveside readings from the Koran.
Mousavi and Karroubi stood against Ahmadinejad in the vote and have waged a defiant campaign since his re-election which Mousavi has described as a "shameful fraud."
The crisis is the worst in the 30-year history of the Islamic republic and created deep rifts among the nation's ruling elite.
|A picture released by Gooya News allegedly shows Iranian demonstrators as they stand opposite riot policemen during a commemoration for people killed in election violence in Tehran.|
In the latest show of defiance, thousands of people flashing victory signs gathered around Vali Asr street and the Grand Mosalla open-air religious venue.
"Some protesters also set fire to roadside rubbish bins, while anti-riot police on motorbikes rode into the crowds in an attempt to disperse them," a witness said. "Police also smashed window panes of several cars."
A motorbike was said to have been set alight and hundreds of motorists sounded their car horns, a protest tactic regularly used by Mousavi supporters.
The foreign press remains banned from covering such demonstrations as part of tough restrictions imposed in the post-election turmoil.
Hundreds of thousands of people had taken to the streets after the election and in the ensuing violence about 30 people were killed, scores wounded and several thousand arrested, Iranian officials say.
The political crisis has also seen Ahmadinejad come under fire even from his own supporters and he has been warned to obey supreme leader Ayatollah Ali Khamenei or face the consequences.
In recent days, the authorities have made gestures towards the opposition, including releasing about 140 protesters and promising to free more of the some 250 still behind bars.
One of those arrested, prominent Iranian reformist Saeed Hajjarian, was removed from jail and transfered to a government-owned residential complex despite a judicial order to set him free, a lawmaker said on Thursday.
Twenty "rioters" are due meanwhile to go on trial from Saturday on charges including attacks on government and military offices and contact with "enemies" including exiled opposition group the People's Mujahedeen.