Syrian troops have shelled a volatile area and carried out sweeping raids, one day after security forces killed about 40 people in one of the deadliest crackdowns in months in the country's uprising, activists said.
The Syrian opposition's two main activist groups, the British-based Syrian Observatory for Human Rights and the Local Co-ordinating Committees, said shells slammed into the Baba Amr district of Homs. Raids and arrests also were reported around the eastern city of Deir el-Zour.
Activists said there were casualties, but their number was not immediately clear.
The popular revolt against Syrian President Bashar Assad's regime has proved remarkably resilient over the past seven months, with protests erupting every week despite the near-certainty that the government will respond with bullets and tear gas. The UN estimates the regime crackdown on the protests has killed 3,000 people since March.
Much of Friday's bloodshed happened after protests had ended and security forces armed with machine guns chased protesters and activists, according to opposition groups monitoring the demonstrations. Authorities disrupted telephone and internet service, they said. At least 40 people were killed, according to the observatory and the LCC.
Syria has largely sealed off the country from foreign journalists and prevented independent reporting, making it difficult to confirm events on the ground. Key sources of information are amateur videos posted online, witness accounts and details gathered by activist groups.
The regime appears to lack sufficient numbers of loyal troops to garrison all the centres of unrest at the same time, so government forces will often sweep through an area in the wake of protests, breaking up new gatherings and hunting activists, before being deployed elsewhere.
The result has been a months-long stalemate. Nevertheless, the capture and subsequent death of Libya leader Muammar Gaddafi, under still-unclear circumstances, has energised the opposition. Last week, thousands of Syrians took to the streets shouting that Mr Assad will be next.
On Friday, many protesters said they wanted a no-fly zone established over Syria to protect civilians in case the Syrian regime considers attacking protesters from the sky, the activist groups said.
The protesters also called for international monitors, although most opposition groups reject the idea of foreign military intervention. The Syrian government insists the unrest is being driven by terrorists and foreign extremists looking to stir up sectarian strife.