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 after some 3,000 protesters, many wearing black, chanted "Death to the dictator!" and "Death to dictatorship!" near Revolution Square in downtown Tehran. Police fired tear gas, water cannons and guns but it was not clear if they were firing live ammunition.
Some protesters appeared to be fighting back, setting fire to militia members' motorcycles, witnesses said. Helicopters hovered, ambulances raced through the streets and black smoke rose over the city.
Police and militia were blocking protesters from gathering on the main thoroughfare running east from Revolution Square to Freedom Square, the witnesses said.
A massive rally in Freedom Square Monday set off three consecutive days of protests demanding the government cancel and rerun June 12 elections that ended with a declaration of overwhelming victory for hardline President Mahmoud Ahmadinejad. Reformist presidential candidate Mir Hossein Mousavi says he won and Ahmadinejad stole the election through widespread fraud. Mousavi has not been seen since or issued public comment since a rally Thursday.
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.
Supreme Leader Ayatollah Ali Khamenei sternly warned opposition leaders Friday to end street protests or be held responsible for "the bloodshed, the violence and rioting" to come. The statement effectively closed the door to Mousavi's demand for a new election, ratcheting up the possibility of a violent confrontation.
As reports of street clashes became public, Iran's English-language state TV said that a suicide bombing at the shrine of Ayatollah Ruhollah Khomeini about 12 miles (20 kilometers) south of central Tehran had killed one person and wounded eight. The report could not be independently confirmed due to government restrictions on independent reporting.
The channel also confirmed that police had used batons and other non-lethal weapons against what it called unauthorized demonstrations.
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 witnesses told The Associated Press that between 50 and 60 protesters were hospitalized after beatings by police and pro-government militia. People could be seen dragging away comrades bloodied by baton strikes.
Police clashed with protesters around Tehran immediately after the presidential election. Gunfire from a militia compound left at least seven dead, but further force had remained in check until Saturday.
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.
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 a warning to Mousavi that he would be held responsible if he encouraged protests.
Tehran University, which sits in the heart of downtown Tehran, was cordoned off by police and militia while students inside the university chanted "Death to the dictator!" witnesses said.
Shouts of "Viva Mousavi!" also could be heard. 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 self-described "Green Wave" movement.
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.
"I think the regime has taken an enormous risk in confronting this situation in the manner that they have," said Mehrdad Khonsari, a consultant to the London-based Center for Arab and Iranian Studies.
"Now they'll have to hold their ground and hope that people don't keep coming back. But history has taught us that people in these situations lose their initial sense of fear and become emboldened by brutality," he said.
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.
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.
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 normally for many days, and cell phone service in Tehran is frequently down.
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."
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 was even becoming difficult to reach people close to Mousavi. He said he had not heard from Mousavi's camp since Khamenei's address.
Associated Press Writer William J. Kole in Cairo contributed to this report.
(Copyright 2009 by The Associated Press. All Rights Reserved.)