Shiite gunmen took position during clashes in the Mazra'a area in Beirut on Friday

BEIRUT, Lebanon — Heavily armed Hezbollah fighters seized control of much of western Beirut on Friday, patrolling the deserted streets in a raw show of force that underscored the militia’s refusal to back down in its escalating confrontation with the American-backed government.

Hezbollah allies also forced a government-allied satellite television station off the air and burned the offices of its newspaper affiliate, as Sunni fighters loyal to the government largely melted away after three days of the worst sectarian clashes Lebanon has seen since its 15-year civil war.

Those humiliating blows made clearer than ever the power and determination of Hezbollah, a Shiite group backed by Iran and Syria, and its allies. By Friday afternoon, armed Shiite fighters were riding joyfully through west Beirut in a long column of trucks, cars and scooters, shouting and firing their weapons into the air in a raucous victory celebration.

The government majority issued an urgent appeal for help from other nations on Friday evening, calling Hezbollah’s actions an “armed coup” against Lebanon and its democratic system using “weapons sent by Tehran.” Some government lawmakers, including the Druse leader, Walid Jumblatt, and Saad Hariri, the son of the assassinated former prime minister Rafiq Hariri, spent the day holed up in their compounds, protected by Lebanese Army contingents and the police.

In Washington, Secretary of State Condoleezza Rice said the United States was “deeply concerned” about the continuing violence and condemned Hezbollah as “undermining the legitimate authority of the Lebanese government.”

Ms. Rice and other Bush administration officials were on the phone Friday with their counterparts in Saudi Arabia, Egypt and Lebanon. A senior administration official said the United States, which barely talks to Syria, Iran or Hezbollah, which the Bush administration considers a terrorist organization, was trying to use its Arab allies to send a message to Iran and Syria to stop interfering in Lebanon.

Israeli officials said they were closely tracking events across their northern border but keeping their response muted, clearly anxious not to throw any fuel on the fire.

The gun battles of the past three days have pitted Sunni Muslims against Shiites, with Lebanon’s divided Christians — including Michel Aoun, the former general who is allied with Hezbollah — sitting out the conflict. The clashes appear to be sharply exacerbating sectarian tensions among Muslims here in an ominous echo of the civil conflict in Iraq.

By Friday evening, the conflict had spread to Lebanon’s small but influential Druse community, as a gun battle broke out between supporters of the government and opposition in the Chouf mountains, the Druse heartland. Two people were killed, witnesses said.

It was not yet clear what Friday’s events would mean for Lebanon’s political future, or how Hezbollah’s show of force might translate into a corresponding political advantage. For now, they seemed only to deepen the political stalemate here. For 17 months, Lebanon has been divided between the Hezbollah-led opposition and the government of Prime Minister Fouad Siniora, which is supported by the West and Saudi Arabia. The standoff has left the country without a president since late November.

Lebanon’s army — the one institution viewed as neutral in the country’s bitter political struggle — has stood by during the clashes, unwilling to take sides. Hezbollah and its allies handed control of some government offices to the army on Friday after commandeering them, hoping to burnish Hezbollah’s nationalist credentials.

Three days of street battles here have left at least 11 people dead and 20 wounded. Most of the fighting has been in Beirut, but there have been sporadic gun battles between pro-government and opposition forces in other areas, including the Bekaa Valley, northern Lebanon and the Chouf mountains.

The violence seemed to be tapering off on Friday, though some major roads remained blocked, including the one linking Beirut and its airport.

The recent battles started after the government on Tuesday took steps against Hezbollah’s private telecommunications network, calling it a violation of Lebanon’s sovereignty.

The majority appears to have believed it could pressure Hezbollah, which has been reluctant in the past to use its military force domestically, said Sarkis Naoum, a senior columnist for Al Nahar newspaper.

But in fact, Hezbollah — impatient with the long stalemate — was waiting for just such an opportunity to demonstrate its power, Mr. Naoum said.

Hezbollah loyalists quickly blocked roads in the capital with burning tires, including the crucial road to the airport. On Thursday, Hezbollah’s leader, Sheik Hassan Nasrallah, said the government had declared war by threatening to shut down the group’s private telephone network. “We have said before that we will cut the hand that targets the weapons of the resistance,” he said, speaking by video link. “Today is the day to fulfill this promise.”

The group will call off its fighters only after the government backs down completely from its challenge to the telephone network, Sheik Nasrallah said.

But Hezbollah’s goals are likely to extend beyond that, said Amal Saad-Ghorayeb, a Hezbollah expert.

“I can’t envision Hezbollah joining this government, so the demands will go beyond their previous demands,” she said. “They want the government to resign. This is effectively a coup.”

The government has been urging the election of the army commander, Gen. Michel Suleiman, as president, and on Thursday, Saad Hariri, a leader of the government political alliance, repeated that proposal. But Hezbollah and its Christian allies have rejected proposals for electing a president until there is a much broader agreement, including a new cabinet and a new election law.

In Friday’s clashes, Hezbollah and its allies appear to have singled out Mr. Hariri, the leader of the pro-government March 14 political alliance. Militia fighters fired rocket-propelled grenades at the office of his Future newspaper in west Beirut early on Friday morning, badly burning several floors of the building. The Future Movement’s television station was forced off the air, and the Lebanese Army took over another Future office after Hezbollah allies made threats against it.

One casualty of the recent confrontations has been the widespread notion that Sunni militias capable of countering Hezbollah were being trained in Lebanon, said Mr. Naoum, the columnist.

As it turned out, the young Sunni fighters loyal to Mr. Hariri’s Future Movement — part of the government majority — were no match for their better-armed Shiite rivals. Mr. Hariri apparently recognized this, and ordered a withdrawal rather than face a massacre. On Friday, numerous men in the Sunni neighborhood of Tarik Jadideh complained that they had been given instructions not to fight, and now felt humiliated.

“Saad Hariri let us down,” said one young man in Tarik Jadideh, where the streets were still littered with broken glass on Friday, and blackened building facades bore witness to fierce battles the night before with rocket-propelled grenades and small arms. “We don’t want the Future Movement any more, or the whole Hariri family.” The man refused to give his name, because Mr. Hariri is such an important figure in the area.

Another young man added: “What happened last night around midnight is that orders were given to desert our positions and go home. They put us on the front line of the confrontation and then abandoned us 15 minutes later.”

So far, the young men — some in their teens — who make up most of the militia fighters have obeyed commands from their leaders to stop fighting. Whether they will continue to do so is a much-discussed question here.

Hweida Saad contributed reporting from Beirut, Isabel Kershner from Jerusalem, and Helene Cooper from Washington.