Beirut: Syrian security forces killed more than 20 people on Friday and authorities disrupted telephone and Internet service in restive areas during mass protests calling for the downfall of President Bashar Assad's regime, activists said.

Syria's uprising has proved remarkably resilient over the past seven months, with protests erupting every week to denounce the regime. The UN estimates the government crackdown on the protests has killed 3,000 people since March.

Friday’s death toll was more than 20, according to two main activist groups, the British-based Syrian Observatory for Human Rights and the Local Coordinating Committees.

Syria has largely sealed off the country from foreign journalists and prevented independent reporting, making it difficult to confirm events on the ground.

Communications were spotty Friday in the Damascus suburb of Douma and the central city of Homs, which have seen major anti-government protests, activists said. The move appeared to be an attempt to cut off the opposition's ability to organize and report on the protests.

Deaths were mostly in Homs and Hama in central Syria. "There was a very fierce reaction to the protests in Homs on Friday," said Syria-based activist Mustafa Osso. Syrian forces opened fire as some 2,000 people gathered for protests, he said.

"There are many injured as well. Hospitals are having a hard time coping with the casualties," Osso said.

Majd Amer, an activist in Homs said sporadic gunfire could be heard as protesters poured out of mosques following Friday prayers.

It is difficult to gauge the strength of the revolt in Syria, a country of 22 million people. The crackdown does not appear to have significantly reduced the number of protests, but neither does the regime appear to be in any imminent danger of collapse.

The regime appears to lack sufficient numbers of loyal troops to garrison all the centers 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. Still, the capture and subsequent death of Libya's Moammar Gadhafi, under still-unclear circumstances, has energized the opposition. Last week, thousands of Syrians took to the streets shouting that Assad will be next.

The protests come amid efforts by the Arab League to end the bloodshed, and debates within the opposition on how to bring international pressure to bear on the regime.

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.