Syrian troops killed and wounded scores of people Friday when they opened fire on a large anti-government demonstration in the central city of Hama, one of numerous protests held as Syrians poured onto the streets in towns and cities around the country to stage what activists claimed was the biggest effort yet to force the ouster of Syrian President Bashar al-Assad.

With the Internet completely shut down by the government for the first time in almost all locations nationwide and most journalists banned from entering Syria, it was impossible to verify the assertions made by human rights groups and witnesses.

But it appeared that the biggest demonstrations and the worst violence occurred in Hama, a city whose name is indelibly associated in the minds of most Syrians with an earlier uprising three decades ago that ended only after Syrian troops killed as many as 30,000 people and razed large portions of the city.

Witnesses said between 50,000 and 100,000 people had gathered in a central square Friday when security forces began raking the crowds with live ammunition. The Local Coordinating Committee, a group that represents the multiple committees formed to organize protests in locations around the country, said it had confirmed the names of 54 people who were killed, and some witnesses said the toll was higher.

One man who participated in the protest and was contacted by telephone said more than 100,000 people were marching through the streets when the security forces opened fire.

“We were carrying flowers and chanting for freedom,” said the man, who put the death toll at 67. “They just started shooting from every direction.” Many bodies were still lying in the streets, he said, because the security forces were preventing ambulances from reaching the victims, who were being taken to the hospital by private cars and motorcycles.

The violence did not appear to deter the protesters, however, and a video posted on YouTube on Friday night showed a big crowd of protesters marching along a Hama street hours after the killing had taken place.

The scale of the Hama protest, and reports of numerous other large demonstrations, suggested that the protest movement is gaining renewed momentum 11 weeks after demonstrators first took to the streets in Syria. Although the demonstrations that have erupted spontaneously across most parts of the country have been widespread, they have typically not numbered more than a few thousand people, denying the protest movement the momentum that brought about the fall of presidents in Tunisia and Egypt earlier in the year.

Friday’s protests were inspired in part by anger at the apparent torture death of a 13-year-old boy, Hamza Ali al-Khateeb, whose mutilated body was returned to his family last week, a month after he had been detained by the security forces. Video of the corpse was posted on YouTube, turning the boy into a symbol of the government’s brutality.

Activists dubbed Friday “Children of Freedom Friday” in honor of all child victims of the government crackdown. There were calls for renewed demonstrations Saturday to protest the killings in Hama.

There were also signs of building frustrations as the confrontation between the Syrian security forces and protesters entered its 12th week. In the southern town of Daraa, protesters angrily burned the flags of Iran, China and Russia, three countries perceived to be supporting the Syrian government, according to a video posted on YouTube.

In Homs, Syrian state TV reported that protesters set fire to government buildings, something confirmed by an activist in the town, who was contacted by telephone.

“Those buildings are being used to kill people,” he said. “Naturally some had a reaction. We see it as an essential self-defense.”

A special correspondent contributed to this report.