With shouts of "Syria out!" 25,000 protesters massed outside Parliament in a dramatic display of defiance that forced out Lebanon's pro-Syrian prime minister and Cabinet Monday, two weeks after the assassination of a popular politician touched off increasing unrest.

Minutes after Prime Minister Omar Karami (search) announced he was stepping down, jubilant demonstrators — shouting, waving flags and handing red roses to soldiers — demanded that Syrian-backed President Emile Lahoud (search) bow out, too, and pressed on with their calls for Syria to withdraw its troops from the country.

Syria remained silent about the rapidly changing atmosphere in Beirut, where it ruled unopposed for years, even deciding on Lebanon's leaders, after deploying troops ostensibly as peacekeepers during the 1975-90 civil war.

But the dramatic developments — reminiscent of Ukraine's peaceful "orange revolution" and broadcast live across the Arab world — could provoke a strong response from Syria, which keeps 15,000 troops in Lebanon. It also could plunge this nation of 3.5 million back into a period of uncertainty, political vacuum or worse.

Like their counterparts in Ukraine, the Lebanese demonstrators took their ground and held it — they planned to stay in Beirut's central Martyrs' Square (search) again Monday night. And like Ukraine, their movement had trademark colors: the bright red and white of the Lebanese flag, waved high in the air and worn as a scarf.

The White House welcomed Karami's resignation, saying it opens the door for new elections that are "free of all foreign interference" from Syria, but called again on Damascus to pull out its soldiers.

"Syrian military forces and intelligence personnel need to leave the country," said White House spokesman Scott McClellan said. "That will help ensure that elections are free and fair."

In one sign Syria has no intention of just packing up and leaving, Syrian President Bashar Assad (search) said in remarks published Monday that there will be a price for Syrian troop withdrawal: a settlement with Israel.

"Under a technical point of view, the withdrawal can happen by the end of the year," Assad told the Italian newspaper La Repubblica. "But under a strategic point of view, it will only happen if we obtain serious guarantees. In one word: peace."

At first glance, the resignation of Karami and his government was a huge victory for the opposition, united by dislike of the Syrians, the Syrian-backed government and the drive to find those who killed former Prime Minister Rafik Hariri two weeks ago. Many blame Syria for his assassination.

A series of protests have shaken Lebanon since Hariri, the nation's most prominent politician, was killed by a bomb in Beirut Feb. 14. Sixteen others also died.

The government may have stepped down, at least in part, in hopes of quelling the unprecedented anger at Syria and its allies in Lebanon. Despite the resignation, Damascus remains the major player in Lebanon: aside from its troops, it has powerful allies, including the president, the intelligence services and the military.

President Lahoud quickly accepted the resignation of Karami's 4-month-old Cabinet — which replaced Hariri's government — and asked Karami to stay on in a caretaker capacity until a new government is formed.

But opposition leaders — a diverse group of Muslim, Druse and Christians — demanded a neutral government to organize parliamentary elections this spring and to investigate Hariri's murder.

Druse opposition leader Walid Jumblatt, responding to Assad's published remarks, said Lebanon "cannot wait for peace to be achieved" in the Middle East and demanded a speedy troop withdrawal.

The State Department's annual report on human rights abuses around the world, released Monday, called the events in Lebanon a "Cedar Revolution" — a moniker that brings the country in line with Czechoslovakia's Velvet Revolution, Georgia's Rose Revolution, and Ukraine's Orange Revolution.

"In Lebanon, we see growing momentum for a Cedar Revolution that is unifying the citizens of that nation to the cause of true democracy and freedom from foreign influence," Undersecretary of State Paula Dobriansky said, referring to the majestic tree that is celebrated in the Bible as a symbol of well-being and appears on Lebanon's flag.

Monday's demonstration came exactly two weeks after Hariri's slaying. Banks, businesses and most schools were closed to protest the killing. Among the demonstrators were lawyers in black court robes, doctors in white coats, businessmen, housewives and students.

Hundreds of soldiers and police ringed Martyrs' Square, but there was no violence, even as more and more protesters evaded the cordon and join the demonstration. Protest leaders urged their followers not to provoke the security forces, and some security officers appeared to sympathize with the illegal demonstration.

Protesters gave red roses to some soldiers, and sang the national anthem and chanted: "Syria out!" and "We want no other army in Lebanon except the Lebanese army!"

At the nearby Parliament building, Karami had asked the legislature for a vote of confidence. Even though he almost certainly would have won, he resigned instead of calling the vote.

In announcing his resignation, Karami said he did it for the good of Lebanon after withstanding unjust criticism of his government in the parliamentary debate.

"I am keen that the government will not be a hurdle in front of those who want the good for this country. I declare the resignation of the government that I had the honor to head. May God preserve Lebanon," Karami said in remarks heard through loudspeakers and watched on a giant screen by throngs on the Martyrs' Square.

Demonstrators immediately shouted for Lahoud to step down, and speakers urged them to stay put until heads of the security agencies resign as well. The demonstrators also called for the Syrian intelligence chief to leave and for the Syrian army to withdraw.

"Lahoud, your turn is coming!" the crowd shouted.

Lahoud's six-year term was renewed in September by Parliament, under apparent Syrian pressure, in defiance of a U.N. resolution that demanded Lebanon hold presidential elections and the withdrawal of Syrian troops.

While Karami's Cabinet continues as a caretaker government, the president consults with parliament then appoints a new prime minister. That person consults parliamentary blocs to form a Cabinet, which must withstand a parliamentary vote of confidence. Normally, the process takes a few weeks.

Opposition leaders were quick to try to quiet any qualms in Damascus.

"We don't want this victory to be a defeat for Syria," legislator Ghazi Aridi told the crowd.

And Jumblatt, who has been holed up at his ancestral home in the mountains for fear of assassination, said: "We reject any animosity toward Syria. We want a correct relationship."