By Middle East correspondent Anne Barker, wires
Syrian tanks have moved into the flashpoint towns of Daraa and Douma, where witnesses say there are new casualties as troops fire indiscriminately around the town.
Rights activists say at least 25 people have been killed and many more injured as thousands of Syrian troops swept into the towns on Monday (local time).
Daraa, in the far south, is where the wave of anti-government protests in Syria began more than five weeks ago.
Witnesses there report thousands of troops have begun attacking the town, killing and wounding an unknown number of people and leaving bodies lying in the streets.
Rights activists say snipers have taken up positions on rooftops.
The activists said the exact number of casualties was difficult to establish as the snipers made it impossible to reach them.
"Bodies are lying in the streets and we can't recover them," one activist said.
Another witness spoke of five people killed in Daraa when their car was raked by gunfire.
"We saw with our own eyes, they were in a car that was riddled with bullets," the witness said, adding that he was on a rooftop and could hear intense gunfire reverberating across the southern town near the Jordanian border.
"The minarets of the mosques are appealing for help. The security forces are entering houses. There is a curfew and they fire on those who leave their homes. They even shot at water tanks on roofs to deprive people of water."
Not long after the troops swept into Daraa, neighbouring Jordan announced Syria had sealed off its border with the kingdom. The move, to prevent people from fleeing the country, has been denied by Syria.
A massive crackdown was also underway in Douma, 15 kilometres north of Damascus, a rights activist said.
"Security forces have surrounded a mosque and are firing indiscriminately. Streets are cut off from each other and Douma is isolated from the outside world," the activist said, adding that there have been sweeping arrests in the town since Sunday.
He said communication network was also cut in the town, as he spoke from the edge of Douma.
The latest crackdown appears to be in retaliation for massive protests on Friday, in which tens of thousands of Syrians took to the streets demanding the fall of president Bashar al Assad's regime.
There are also reports of security forces raiding homes in two towns near the capital Damascus and rounding up opponents of the regime.
"There are injured people. Scores have been arrested. The security [forces] are repeating the same pattern in all the centres of the democratic uprising. They want to put down the revolution using the utmost brutality," the rights campaigner said from Damascus.
The campaigner said all telecommunications with the Damascus suburb of Douma had been cut, but one activist managed to escape the suburb after the attack began just before dawn on Monday and report on the situation.
At least 135 people are reported to have died since Friday, when security forces opened fire on huge protests and then attacked mourners who turned out on Saturday to bury the dead.
More than 350 civilians are believed to have been killed since unrest first broke out in Daraa on March 18.
Meanwhile, the Syrian Observatory for Human Rights says at least 13 civilians have been shot dead since security forces launched an attack on the coastal town of Jabla on Sunday.
The mass demonstrations around the country came despite Mr Assad signing decrees on Thursday ending a draconian state of emergency.
Activists say the violence the following day, when 100 people were killed during protests across the country, showed he was not serious about addressing calls for political freedom.
But despite the crackdowns the protests show no sign of abating, with pro-democracy activists renewing calls for action.
Western governments, including Australia, are urging their citizens inside Syria to leave immediately, saying the security situation is becoming increasingly volatile.
- Australian Broadcasting Corporation
- © ABC