Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. Opposition Web Sites: 4 Iranian Activists Killed in Clashes With Security Forces Killing comes as thousands of reformists rally in central Tehran's Engelab Square in defiance of police warnings VOA News 27 December 2009 Iranian opposition Web sites say four opposition activists have been killed in a second day of clashes with security forces in the capital, Tehran. The opposition groups say the four protesters were killed Sunday as thousands of reformists rallied in central Tehran's Engelab Square in defiance of police warnings. Witnesses say demonstrators chanted "death to the dictator" - a reference to Iran's conservative leadership. They say police fired tear gas and used batons to disperse the protesters. Iranian reformists have been staging regular mass protests against the disputed June re-election of conservative President Mahmoud Ahmadinejad. Iran's opposition says the vote was rigged, a charge the government denies. Iranian police chief Esmail Ahmadi-Moqadam had warned the opposition against holding rallies Sunday to coincide with national observances of Ashura, a Shi'ite Muslim festival. On Saturday, Iranian police used tear gas and batons against demonstrators who gathered at a north Tehran mosque where reformist former President Mohammad Khatami was giving a speech. A reformist Web site said pro-government activists tried to disrupt the event. Video showed outsiders entering the mosque amid shouts from those inside. Opposition groups also said security forces beat up and arrested protesters in central Tehran Saturday. During Ashura, Shi'ite worshippers mourn the seventh-century killing of Imam Hussein, the grandson of the Prophet Muhammad. Last Monday, hundreds of thousands of people attended the funeral of dissident cleric Grand Ayatollah Hossein Ali Montazeri in the city of Qom and used the occasion to chant anti-government slogans. Iranian authorities cracked down on protesters at the funeral and at subsequent opposition rallies. Some information for this report was provided by AFP and Reuters. .