TEHRAN: Police beat protesters and fired tear gas and water cannons at thousands who rallied Saturday in open defiance of Iran's clerical government, sharply escalating the most serious internal conflict since the 1979 Islamic Revolution.
Eyewitnesses described fierce clashes near Revolution Square in central Tehran after some 3,000 protesters, many wearing black, chanted "Death to the dictator!" and "Death to dictatorship!" Police fired tear gas, water cannons and guns but it was not immediately clear if they were firing live ammunition.
English-language state TV confirmed that police had used batons and other non-lethal weapons against what it called unauthorized demonstrations.
The witnesses told The Associated Press that between 50 and 60 protesters were seriously beaten by police and pro-government militia and taken to Imam Khomeini hospital in central Tehran. People could be seen dragging away comrades bloodied by baton strikes.
Some protesters appeared to be fighting back, setting fire to militia members' motorcycles in streets near Freedom Square, witnesses said.
Helicopters hovered over central Tehran. Ambulance sirens echoed through the streets and black smoke rose over the city.
Tehran University was cordoned off by police and militia while students inside the university chanted "death to the dictator!" witnesses said. Police and militia barred people from entering Freedom Street, which runs from Freedom Square to Revolution Square, to prevent a massive gathering, the witnesses said.
Amateur video showed dozens of Iranians running down a street after police fired tear gas at them. Shouts of "Allahu Akbar!" — "God is Great" — could be heard on the video, which could not be independently verified.
The English-language state channel said a blast at the Tehran shrine of Ayatollah Ruhollah Khomeini had killed one person and wounded two but the report could not be independently confirmed due to government restrictions on independent reporting. The shrine is about 12 miles (20 kilometers) south of central Tehran.
Hundreds of thousands of supporters of reformist presidential candidate Mir Hossein Mousavi took to the streets for four consecutive days this week demanding the government cancel and rerun June 12 elections that ended with a declaration of overwhelming victory for hardline President Mahmoud Ahmadinejad. Mousavi says he won and Ahmadinejad stole the election through widespread fraud.
Supreme Leader Ayatollah Ali Khamenei sided firmly with Ahmadinejad on Friday, saying the vote reflected popular will and ordering opposition leaders to end street protests or be held responsible for any "bloodshed and chaos" to come.
The statement effectively closed the door to Mousavi's demand for a new election, ratcheting up the possibility of a violent confrontation.
Police had clashed with protesters around Tehran immediately after the vote, and gunfire from a militia compound left at least seven dead, but the full force of the state remained in check until Saturday.
Web sites run by Mousavi supporters had said he planned to post a message, but there was no statement by the time of the planned street protests at 4 p.m. (7:30 a.m. EDT, 1130 GMT). Some pro-reform Web sites called for people to take to the streets.
Witnesses said protesters wore black as a symbol of mourning for the dead and the allegedly stolen election, with wristbands in green, the emblem of Mousavi's "Green Wave" movement.
Tehran Province Police Chief Ahmad Reza Radan said that police would "crack down on any gathering or protest rally which are being planned by some people." The head of the State Security Council also reiterated the warning to Mousavi that he would be held responsible if he encouraged street protests.
Eyewitnesses said thousands of police and plainclothes militia members filled the streets to prevent rallies. Fire trucks took up positions in Revolution Square and riot police surrounded Tehran University, the site of recent clashes between protesters and security forces, one witness said.
All witnesses spoke on condition of anonymity because they feared government reprisals for speaking with the press. Iranian authorities have placed strict limits on the ability of foreign media to cover recent events, banning reporting from the street and allowing only phone interviews and information from officials sources such as state TV.
The government has blocked Web sites such as BBC Farsi, Facebook, Twitter and several pro-Mousavi sites that are conduits for Iranians to tell the world about protests and violence.
Text messaging has not been working in Iran since last week, and cell phone service in Tehran is frequently down.
Mousavi and the two other candidates who ran against Ahmadinejad had been invited to meet with Iran's Guardian Council, an unelected body of 12 clerics and Islamic law experts close to Khamenei that oversees elections. Its spokesman told state TV that Mousavi and the reformist candidate Mahdi Karroubi did not attend.
The council has said it was prepared to conduct a limited recount of ballots at sites where candidates claim irregularities but Mousavi's supporters did not withdraw his demands for a new election.
A spokesman for Mousavi said Friday the opposition leader was not under arrest but was not allowed to speak to journalists or stand at a microphone at rallies. Iranian filmmaker Mohsen Makhmalbaf told the AP from Paris it's even becoming difficult to reach people close to Mousavi. He said he has not heard from Mousavi's camp since Khamenei's address.
Both houses of the U.S. Congress approved a resolution on Friday condemning "the ongoing violence" by the Iranian government and its suppression of the Internet and cell phones.
In an interview taped Friday with CBS, Obama said he is very concerned by the "tenor and tone" of Khamenei's comments. He also said that how Iran's leaders "approach and deal with people who are, through peaceful means, trying to be heard" will signal "what Iran is and is not."