President Bashar Assad's forces renewed their assault on towns seen as key to the demonstrations calling for an end to his family's 40-year rule.

The regime also cut Internet service across most of the country, a potentially dire blow for a movement that motivates people with graphic YouTube videos of the crackdown and loosely organizes protests on Facebook pages.

The Internet shutdown, if it continues, could also hamper the movement's ability to reach the world outside Syria, where the government has severely restricted the media and expelled foreign reporters. Still many activists found alternate ways to log on and upload videos, such as satellite connections.

Rami Abdul-Rahman, director of the Syrian Observatory for Human Rights, said tens of thousands of people were protesting in Hama when security forces opened fire.

There were protests in towns and cities across the country. Protesters also gathered in several Damascus suburbs, as well as the capital's central Midan neighborhood.

Abdul-Rahman said security forces killed one person in the village of Has in the northern province of Idlib. Another rights activist, Mustafa Osso said security forces shot dead three protesters in the northeastern city of Deir El-Zour. State-run TV said five policemen were wounded there but did not say how.

"It is a real massacre. It is terrorism by itself and they want the people to stay silent," said an activist in Hama. The activist said hospitals were calling on people to donate blood.

Syria's state-run TV said three "saboteurs" were killed when police tried to stop them from setting a government building on fire in Hama. The Syrian government blames armed gangs and religious extremists for the violence.