TEHRAN (Reuters) - An Iranian opposition website said three opposition supporters were killed when police opened fire on Sunday in a second day of clashes in Tehran during a major Shi'ite religious festival.
"Three people were killed and two others were wounded when police opened fire at protesters," the Jaras website said in a report that could not be immediately independently verified.
Foreign media have been banned from reporting directly from opposition demonstrations after Iran's disputed June election.
Jaras later said shooting was heard in an area of central Tehran some distance from where it had reported that the three people were killed.
"Gunfire was heard in the Enqelab square as well. Protesters are chanting 'Death to the Dictator'," it said.
The same website earlier said security forces fired tear gas to disperse opposition supporters in downtown Tehran.
It said protesters set one police motorbike on fire. A plume of black smoke could be seen above the centre of the city, Jaras added, as police blocked streets in the area and clashes intensified.
The reported unrest underlined escalating tension in the Islamic Republic six months after a disputed presidential election plunged the major oil producer into turmoil and exposed splits within the clerical and political establishment.
A witness told Reuters there was a heavy presence of both security forces and opposition backers in central Tehran, a city of around 12 million people
"Police prevented groups of protesters from joining each other," she said.
Other witnesses said thousands of pro-government Iranians were also gathering in central Tehran.
The authorities have warned the pro-reform opposition against using a two-day major Shi'ite Muslim religious mourning ritual on Dec. 26-27 to revive protests against the clerical establishment, six months after June's disputed election.
Police helicopters were seen flying overhead in Tehran.
Jaras earlier said hundreds of riot police were deployed in central Tehran to prevent demonstrations planned by opposition supporters during Ashura, when Shi'ite Muslims commemorate the 7th century death in battle of a grandson of Prophet Mohammad.
(Editing by Angus MacSwan)