Most Internet services in Syria were cut off on Thursday, with cell phone signals also disrupted, U.S. technology companies monitoring the war-torn country's web traffic said.

Starting at 12:26 p.m. local time (1026 GMT), Syria's international Internet connectivity has been shut down.

"In the global routing table, all 84 of Syria's IP address blocks have become unreachable, effectively removing the country from the Internet," U.S. company Renesys said on its website.

According to Syrian activists, Syrian government often cuts Internet and phone services before launching major military operations, which on Thursday prompted speculations of imminent offensives by government troops.

During the day, government troops and opposition forces have engaged in clashes near the capital, which cut off the road to Damascus airport.

Earlier on Thursday, an explosive device went off near the house of a leading member of Syria's ruling al-Baath party in the southern province of Daraa, killing three policemen and injuring others. The explosive device, weighing 50 kg, went off in front of the house of a secretary of al-Baath party in Daraa, causing damage to nearby buildings.

On Wednesday, a car bomb rattled the Busra town on the countryside of Daraa and killed two people.

The fighting has intensified between government troops and Western-backed rebels who are trying to erode Syrian government's grip on the capital and elsewhere in Syria in the hope of hastening the collapse of the Syrian administration. Endi