Hundreds of thousands of protesters from Hezbollah and its pro-Syrian allies massed Friday in downtown Beirut seeking to force the resignation of Western-backed Prime Minister Fuad Saniora, who was holed up in his office ringed by hundreds of police and combat troops.

The protest, which police estimated at 800,000, created a sea of Lebanese flags that blanketed downtown and spilled onto the surrounding streets. Hezbollah officials put the number at 1 million — one-fourth of Lebanon's population.

"Saniora out! We want a free government!" protesters shouted through loudspeakers. The crowd roared in approval amid the deafening sound of Hezbollah revolutionary and nationalist songs. "We want a clean government," read one placard, in what has become the opposition's motto.

Launching a long-threatened campaign to force Lebanon's U.S.-backed government from office, Hezbollah and its pro-Syrian allies said the demonstration would be followed by a wave of open-ended protests. Hezbollah had threatened demonstrations unless it and its allies obtained a veto share of the Cabinet — a demand Saniora and Lebanon's anti-Syrian parties rejected. The protests now aim to generate enough popular pressure to paralyze the Saniora government and force it out.

Heavily armed soldiers and police had closed all roads to downtown, feverishly unfurling barbed wire and placing barricades.

Despite Hezbollah's assurances the protests will be peaceful, the heavy security came amid fears the protests may turn into clashes between pro- and anti-Syrian factions or that Hezbollah supporters could try to storm Saniora's government headquarters.

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Hezbollah's security men, donning caps, formed two lines between the protesters and the security forces to prevent clashes.

"I wish that the prime minister and his ministers were among us today, not hiding behind barbed wire and army armored carriers. He who has his people behind him does not need barbed wire," Michel Aoun, a Christian leader and Hezbollah ally, told the crowd.

Hezbollah's leader Hassan Nasrallah, who has not made a public appearance since a September rally for the militant group, could not be seen Friday.

Inside the prime minister's building, Saniora went about his schedule, in what appeared to be a tactic to ignore the throngs outside. A day earlier, a defiant Saniora vowed his government would not fall but warned that "Lebanon's independence is threatened and its democratic system is in danger."

A demonstration last week for a slain anti-Syrian politician also drew hundreds of thousands of people downtown, filling Martyr's Square. But Friday's appeared larger, as protesters swarmed not only that square but others, as well as nearby streets and parking lots.

Supporters planned to set up camp around the clock in tents erected on a road outside Saniora's office and in a downtown square.

Hezbollah has tried to depict the protest as rallying all Lebanese, not just its supporters. It urged demonstrators to wave only the red and white Lebanese flag with its green cedar tree, in contrast to past protests that featured the group's yellow flag with a fist and Kalashnikov rifle.

The battle is a fallout from the summer war between Hezbollah and Israel that ravaged parts of Lebanon. The guerrilla force's strong resistance against Israeli troops sent its support among Shiites skyrocketing, emboldening it to grab more political power. Hezbollah also feels Saniora did not do enough to support it during the fight.

Pro-government groups, in turn, resent Hezbollah for sparking the fight by snatching two Israeli soldiers, dragging Lebanon into war with Israel.

Government supporters accuse Syria of being behind the Hezbollah campaign, trying to regain its lost influence in its smaller neighbor. Hezbollah and its allies, in turn, say the country has fallen under U.S. domination and that they have lost their rightful portion of power.

Tension have been running high between Sunni Muslims, who generally support the anti-Syrian government, and Shiites, who lead the pro-Syrian opposition, and Lebanon's Christians, who are divided between the two.

In a stark sign of the divide, the spiritual leader of Lebanon's Sunnis, Grand Mufti Mohammed Rashid Kabbani, gave Friday prayers at the prime minister's headquarters in a show of support for Saniora, a Sunni.

"Fear has gripped the Lebanese," Kabbani said, appealing for the protests to end. "The constitution guarantees freedom of expression, but trying to overthrow the government in the street is a call for stirring up discord among people, and we will not accept this."

Hezbollah's deputy leader, Sheik Naim Kassim, made it clear the fight is against "American tutelage" and said the protest action will continue until the government falls.

"We will not let you sell Lebanon, we will protect the constitution and people of Lebanon," Kassim said on television Friday, addressing Saniora.

The United States has made Lebanon a key front in its attempts to rein in Syria and its ally, regional powerhouse Iran. President Bush warned earlier this week that the two countries were trying to destabilize Lebanon.

Lebanon has witnessed a string of assassinations of anti-Syrian figures over the past two years, including a prominent Christian government minister gunned down last week and former prime minister Rafik Hariri, who was killed in a February 2005 bombing.

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