Updated

Nearly 500,000 pro-Syrian protesters and members of Hezbollah (search) descended upon central Beirut (search) on Tuesday, chanting anti-American slogans in an effort to counter weeks of huge rallies demanding the immediate exit of Syrian forces.

Coming just one day after Syrian and Lebanese leaders announced that Syrian forces would begin moving out of Lebanon, the protesters were answering a nationwide call by the militant Shiite Muslim Hezbollah group for the public demonstration.

Organizers handed out Lebanese flags and directed the men and women to separate sections of Riad Solh Square, which is near U.N. offices. Loudspeakers blared militant songs urging resistance to foreign interference. Demonstrators held up pictures of Syrian President Bashar Assad (search) and signs saying, "Syria & Lebanon brothers forever."

Other placards read: "America is the source of terrorism"; "All our disasters are from America"; "No to American-Zionist intervention; Yes to Lebanese-Syrian brotherhood."

Black-clad Hezbollah guards handled security, lining the perimeter of the square and taking position on rooftops. Trained dogs sniffed for bombs.

Large cranes hoisted two giant red-and-white flags bearing Lebanon's cedar tree. On one, the words, "Thank you Syria," were written in English; on the other, "No to foreign interference."

"I ask our partners in the country or those looking at us from abroad: Are all these hundreds of thousands of people puppets? Is all this crowd agents for the Syrians and intelligence agencies?" Hezbollah leader Sheik Hassan Nasrallah (search) said to cheers from the crowd.

At least one opposition leader said the pro-Syrian government pressured people to turn out Tuesday and some reports said Syria bused in people from across the border.

The square was just a few blocks from another downtown square where opposition protesters have been staging protests for days, demanding that Syria (search) withdraw the 14,000 troops it maintains in Lebanon.

Syria's ambassador to the United Kingdom, Sami Khiyami, told FOX News that Syria did not orchestrate Tuesday's demonstrations and noted that many Lebanese have close ties to Syria. He also said that the recent demonstrations calling for Syrian troops to leave Lebanon aren't as anti-Damascus as the media is making them out to be.

"We have pushed Lebanon into stability and security and the majority of Lebanese are thanking us for what we did," Khiyami said. "What we saw yesterday are a mixture of those who oppose Syria and those who are mourning Prime Minister [Rafik] Hariri."

He said Tuesday's demonstrations are not people asking Syria to stay in Lebanon so much, "but in fact to voice their support to the very close ties to Syria."

Cabinet Minister Talal Erslan drew cheers Tuesday when he said the crowd came from all over Lebanon "to affirm our gratitude to Syrian President Bashar Assad."

"We have come here to affirm Lebanon's independence, sovereignty and unity ... and say no to the flagrant foreign interference in our affairs," he said.

Participants stressed that the foreign influence they referred to was from the United States, France and other countries, but not Syria, which they welcomed.

"Syria should not leave. We are one hand and one people," said 16-year-old Esraa Awarki, who traveled by bus from Sharkiya in southern Lebanon. "Why do they want us to split now?"

At one point, the crowd observed a moment of silence for Hariri, whose assassination in a Feb. 14 bombing triggered weeks of anti-Syrian demonstrations. Many Lebanese accuse Syria and Lebanon's government of responsibility for Hariri's death; both deny any involvement.

Bush: Syria Must Withdraw

Hezbollah opposes the U.N. resolution drafted by the United States and France last year calling for Syria to withdraw its 14,000 troops from Lebanon. The proposal also calls for dismantling militias — a point Hezbollah sees as aimed at its well-armed military wing.

In Washington, President Bush demanded again that Syria pull its troops out and allow free elections. "All Syrian military forces and intelligence personnel must withdraw before the Lebanese elections for these elections to be free and fair," he said.

A Syrian official in Damascus said Tuesday that its intelligence agents would be pulled back along with the regular army.

"Of course, all the intelligence personnel will be leaving Lebanon very soon. They are leaving right now" and withdrawing to the Bekaa Valley, Khiyami said.

A Lebanese security source told Reuters that Syrian troops began redeploying to eastern Lebanon in the first stage of the two-phased withdrawal.

"The redeployment to the Bekaa Valley has started in line with the first phase," the source told said. He did not say which positions were being vacated but witnesses reported several troop movements in a mountainous ridge east of Beirut.

"It should be done in a way -- the withdrawal is done in an orderly way -- it is phased but in a rapid timetable so the Syrians are out by the May primary elections," Edwards Djerejian, former U.S. ambassador to Israel and Syria, told FOX News of the Syrian soldiers pulling out of Lebanon.

Djerejian said there is still a risk of the various factions "going at each other" as tensions continue to be heightened but that there is an opportunity to involve all groups in the May elections and democratic process.

"Hezbollah is showing its political muscle today in Beirut," he said, noting that the designated terrorist organization is a political and Shiite party, as well as a militia. "It can also become part of the political process but this is going to take astute leadership."

Hezbollah, founded by Iran and backed in part by Syria, is a key player in the latest political instability, capable of tilting the balance either in favor of the pro-Syrian government or the anti-Syrian opposition.

On Monday, in the biggest demonstration yet of anti-Syrian furor, more than 70,000 Lebanese thronged central Beirut, shouting "Freedom! Sovereignty! Independence!" The demonstrators waved Lebanon's cedar-tree flag and thundered, "Syria out!"

Faced with increasing international pressure and raging Lebanese opposition, Assad on Saturday announced his troops would withdraw after nearly three decades in Lebanon. On Monday, he met with Lebanese President Emile Lahoud (search) in Damascus before both jointly announced a plan.

But the plan sets no deadline for the complete withdrawal of Syrian troops and intelligence agents from Lebanon, and Washington rejected the pullback as insufficient.

The plan also was unlikely to satisfy the Lebanese opposition and the rest of the international community, which have demanded that all Syrian soldiers and an unknown number of intelligence agents leave the country.

Under the plan announced Monday, all Syrian troops in Lebanon would fall back to eastern regions near the Syrian border by March 31. Military officers will decide by the end of April on the duration and size of Syrian forces to remain in that region. After that period, the two governments would decide on a date for pullout.

Syria has had troops in Lebanon since 1976, when they were invited as peacekeepers early in Lebanon's 1975-90 civil war. When the war ended, the troops remained and Syria has dominated Lebanon's politics ever since. Syria had 35,000 troops in the country until 2000, when the majority were withdrawn.

The Associated Press contributed to this report.