BEIRUT, Lebanon - Thousands of Syrians flooded the streets across the country Friday, defying an unrelenting government crackdown that has failed to crush a two-month uprising against the country's authoritarian regime. Human-rights activists said security forces opened fire, killing at least 27 people, including a 10-year-old boy.

Friday's turnout - and the now-familiar, deadly response by the regime - was the latest sign the conflict could be moving toward a dangerous stalemate. President Bashar al-Assad's forces have unleashed tanks and snipers and made thousands of arrests to break the revolt, but protesters continue to face down security forces.

Protesters insisted that their movement was growing and that they would not be bowed.

"We, as young activists, are very optimistic," said a protest organizer in the capital, which saw at least four separate demonstrations Friday - a significant increase from recent rallies in Damascus, the capital and the heart of the regime's power.

Assad has shrugged off U.S. calls to step aside as well as a new round of sanctions targeting him and top aides, suggesting mounting international pressure will not force an end to a crackdown that human-rights groups say has killed at least 900 people since mid-March.

Friday's crushing security response came despite calls a day earlier from President Obama that Assad should lead his country to democracy or "get out of the way." Syria's official news agency said Obama's admonition amounted to "incitement."

The revolt has posed the most serious challenge to the Assad family's 40-year ruling dynasty. When the uprisings sweeping the Arab world reached Syria in mid-March, it appeared to take Assad by surprise. He had enjoyed a degree of popularity in large part because of his anti-Israel views and the reputation of being the only Arab leader willing to stand up to the Jewish state. But his regime's response to the uprising appears to have eroded much of that goodwill.

Still, protesters have yet to bring out the sustained, daily, massive protests that brought down the leaders in Egypt and Tunisia.

Assad's sweeping campaign of intimidation, mass arrests, and heavy security kept crowds last week below earlier levels. But larger and more widespread marches Friday suggest that opposition forces could be trying to regroup.

Witnesses reported protests in the central cities of Homs and Hama, the capital, and its suburbs, and the Mediterranean ports of Banias and Latakia. In the northern city of Aleppo, Syria's second-largest city, security forces using batons quickly dispersed dozens of demonstrators, an activist said.

Human-rights activist Mustafa Osso said the army deployed tanks around the northern town of Maaret al-Numan, which has seen intense protests.

Friday's death toll was reported by the Syrian Observatory for Human Rights.

A 10-year-old boy was among the dead in Homs, Osso said.