BEIRUT, Lebanon — Hundreds of thousands of Hizbollah and allied protesters deluged central Beirut yesterday demanding government change as combat troops added more layers of barbed wire around the offices of the embattled US-backed prime minister who has refused to step down.Some fear the massive, peaceful rally could be a tipping point in the anti-Syrian government’s tense political standoff with the opposition.

Buoyed by the turnout, the pro-Syrian opposition gave Prime Minister Fuad Saniora an ultimatum of a “few days” to accept its demand for a national unity government or face an incessant campaign to oust him.

But Saniora, who has been holed up in his fortified office downtown, refuted the opposition’s demands and asked them to return to the negotiation table.

The opposition should “return to the constitutional institutions to discuss differences and reach real solutions,” he said in a written statement.

Political unrest has split the country along dangerous sectarian lines, with most Sunni Muslims supporting the Sunni prime minister and Shiite Muslims backing the militant Hizbollah. Christian factions are split between the two camps.

But amid the mounting rhetoric and unrelenting protests, there was a glimmer of hope that a settlement could still be reached.

“Hopefully it won’t be long. At the end, there will be no winner, no vanquished. We should all be winners,” Saad Hariri, leader of the anti-Syrian parliamentary majority and a staunch Saniora supporter, told The Associated Press.

Police had no immediate crowd estimates, but yesterday’s rally that filled downtown Beirut’s plazas and many neighbourhoods promised to be one of the biggest in Lebanon’s history. It appeared to be even larger than a similar Hizbollah anti-government rally on December 1 that police said drew 800,000 of Lebanon’s four million people.

In response, pro-government groups staged a rival demonstration that drew tens of thousands in the northern port city of Tripoli.

In Beirut, protesters streamed downtown from all corners of Lebanon, waving Lebanese and Hizbollah flags as loudspeakers blasted anti-government speeches. Musicians pounded drums in a carnival-like atmosphere, while Hizbollah security agents fanned out in the crowd.

“We have come to show them how big our size really is,” said Reem al-Zein, a 20-year-old philosophy student. “I think this lying government will not be able to last much longer after today.”

Sheik Naim Kassem, hizbollah’s deputy leader, said the opposition was willing to stay on the streets for months to achieve its goal.

“Does Bush want popular expression in Lebanon? Does the West and the Arabs want to hear the voice of the people in Lebanon? Tell them ‘Death to America!’ Tell them ‘Death to Israel!”’ the crowd repeated behind him.

Christian opposition leader Michel Aoun, a Hizbollah ally, gave Saniora an ultimatum of “a few days” to either accept a national unity government or face further action.

“What we hope for today is for them to understand that their era is over,” he said in a video link speech that appeared on giant screens, warning that the opposition was committed to “to peaceful means, but even other means are legitimate.”

Press reports have speculated the opposition’s next steps could include a civil disobedience campaign, disruptions of public services and resignations from parliament.

Lebanon’s political crisis began after talks on a national unity Cabinet collapsed and six pro-Hizbollah ministers resigned. It erupted November 21 with the assassination of anti-Syrian politician Pierre Gemayel, followed by a national strike, his funeral and the opposition sit-in.

Relations between the two camps deteriorated after the Israel-Hizbollah war last summer and a UN push for the creation of an international tribunal to try suspects in the 2005 assassination of former Premier Rafik Hariri. Hizbollah’s fight against Israel sent its support among Shiites skyrocketing, emboldening it to grab more political power.

The militant group now accuses Saniora and some elements in his government of working with Israel to destroy the guerrilla force. Pro-government groups, in turn, resent Hizbollah for sparking the war by snatching two Israeli soldiers. They, along with the United States, accuse Hizbollah’s Syrian and Iranian backers of seeking to overthrow the government.

If Saniora heeded Hizbollah’s call and resigned, he would continue in a caretaker capacity until Parliament named a new premier and formed a new Cabinet. But the prime minister has showed no signs of giving in even as Lebanese combat troops and police sealed off major roads and added layers of barbed wire around the his sprawling downtown complex, where he has been living with other Cabinet ministers.

Yesterday, he said he was open to dialogue and acknowledged that the political crisis threatened Lebanon’s security, economy and political system.

“We don’t want Lebanon to be an arena of the wars of others. Lebanon is a nation, not an arena,” Saniora said, in a veiled reference to Syria and Iran.

Saad Hariri also stressed the government was open to giving the opposition their demands if it is part of a package deal that included an agreement on the fate of President Emile Lahoud, support for the international tribunal for his father’s death and implementation of a UN resolution that ended hizbollah’s summer war with Israel.