Fresh clashes broke out between demonstrators and security forces in Tehran on Sunday as large crowds gathered for Ashura, a major religious observance.

An opposition Web site said three people were killed in the fighting. But, with tight restrictions on international media, western media outlets couldn’t independently verify the casualties.

The reformist Web site Parlemannews reported that one of the victims Sunday was Saeed Ali Mousavi, nephew of opposition leader Mir Hossein Mousavi.

Tehran Police Chief Azizollah Rajabzadeh denied that any protesters were killed by security forces.

Police did not fire any shots in Tehran, “and security forces were not in possession of firearms,” Rajabzadeh told the semi-official news agency ISNA.

Since the disputed presidential elections in June, protesters have turned public gatherings into rallies against President Mahmoud Ahmadinejad, who was declared the overwhelming winner of the race.

Police, wary of the potential that Ashura gatherings could present, were out in full force Sunday to quell disruptions, but did not stop demonstrators holding widespread protests.

Near Imam Hussein Square in central Tehran, security forces used tear gas to disperse demonstrators and blocked roads to prevent more from arriving, a witness said.

Protesters seized a motorcycle belonging to a security force member and set it on fire.

Elsewhere in the city, witnesses reported seeing protesters being beaten with batons. Demonstrators chanted “death to the dictator” and some ripped down a picture of Iran’s Supreme Leader Ayatollah Khamenei.

Police helicopters hovered above city squares while small trucks brought in fresh supplies of riot police in parts where clashes were fierce.

Protesters played cat-and-mouse with security forces — gathering, then scrambling and gathering elsewhere.

The unrest followed day-long clashes between the two sides in the streets of Tehran on Saturday.

On Saturday evening, a pro-government mob barged into a mosque where former president and reformist leader Mohammad Khatami was speaking.

The dozens-strong group forced Khatami to end his remarks abruptly when it interrupted the gathering at Jamaran mosque.

Earlier Saturday, scores of security forces on motorcycles charged protesters on sidewalks whenever they started chanting anti-government slogans, witnesses said.

(MORE at CNN)