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. Iran Marks Revolution Anniversary, Cracks Down on Opposition VOA News 11 February 2010 Demonstrators in Tehran Photo: AP An image made from video provided by Iranian State TV, pro-government demonstrators gather in the central square of Tehran to mark the 31st anniversary of Iran's 1979 Islamic Revolution, 11 Feb 2010 Hundreds of thousands of people rallied in the Iranian capital Thursday to mark the 31st anniversary of the Islamic Republic, as security forces cracked down on opposition supporters. Iranian state television showed massive crowds marching to Tehran's Azadi (Freedom) Square to hear a speech by President Mahmoud Ahmadinejad. In his address, Mr. Ahmadinejad praised the achievements of the Iranian people and railed against the West. Meantime, opposition Web sites say security forces fired tear gas to disperse opposition supporters gathered in central Tehran. There are also reports that leading reformist politicians Mehdi Karroubi and former President Mohammad Khatami were attacked. One Web site - Rahesabz - reported that Mr. Khatami's sister-in-law, Zahra Eshraghi, was arrested along with her husband, Mr. Khatami's brother Mohammad Reza Khatami. Eshraghi is the grand-daughter of the founder of the Islamic Revolution, the late Ayatollah Ruhollah Khomeini. The report did not give a reason for her arrest. Top opposition leaders Mir Hossein Mousavi and Karroubi had urged their supporters to turn out on the streets for a peaceful demonstration. An Iranian security official, Police Chief Ismail Ahmadi Moghaddam, told Iranian media Wednesday that authorities are prepared to deal with anyone trying to disrupt state-run rallies. He said several people have already been detained for organizing protests. Mass antigovernment protests broke out after Iran's disputed presidential election in June. Opposition leaders have accused President Ahmadinejad of stealing the vote. The anniversary Thursday marks the 1979 ouster of Iran's monarchist government. Every year, hundreds of thousands of Iranians take part in marches to celebrate the anniversary. There also are reports that Iranian authorities have slowed down Internet service in the country and have blocked Google's e-mail service, Gmail. The California-based Internet company confirmed a sharp drop in e-mail traffic, and acknowledged that users in Iran are having trouble accessing Gmail. In a statement, Google said it believes "people everywhere should have the ability to communicate freely online," adding, "sadly, sometimes it is not within our control." Some information for this report provided by AFP, AP and Reuters. .