Syrian forces pounded the central city of Homs with mortar fire while troops backed by heavy armor stormed rebellious towns across the country on Saturday, leaving six civilians and four soldiers dead, opposition activists said.

Ignoring a UN Security Council call for an end to hostilities, President Bashar Assad's forces clashed with rebel fighters and bombarded several towns and cities, aiming to crush a year-long uprising against the government.

Security forces killed at least one person as they raided Saraqib, in Idlib province bordering Turkey, said the British-based Syrian Observatory for Human Rights (SOHR).

"Sixty per cent of the population of the town of Saraqeb have already fled to areas near the Turkish border," the opposition Syrian Observatory for Human Rights said in a statement.

Activists based in the area told dpa that 26 Syrian tanks had entered the town and started razing houses where rebels were believed to be hiding. Several arrests were made.

"There are dozens of tanks and armored vehicles storming Saraqib now and there is heavy artillery fire," said activist Manhal from Idlib province via Skype.

"A portion of the rebels have made a strategic retreat, but there are rebel forces still inside, and about a third of residents have fled the town," he added.

Two died in Homs, the epicenter of the anti-Assad revolt, as the central city suffered another day of what activists said was indiscriminate gunfire and shelling on residential areas.

"The shelling started like it does every morning, for no reason. They are using mortar and tank fire on many neighborhoods of old Homs," an activist in Homs's Bab Sbaa neighborhood told Reuters by Skype, adding most residents in the area had fled to safer districts and many were trying to get out of the city altogether.

"The Free Syrian Army had been in Bab Sbaa when the army started shelling the area four days ago and they weren't able to block the army raids because they were getting hit by mortars at the same time that armored vehicles were coming in," he said.

"We only have a few rebels here left, there is nothing they can do."

Mortars and heavy artillery fire reportedly hitting the city of Qusair, in Homs province, killed two civilians according to the SOHR, which has a network of contacts across Syria.

In the southern province of Deraa, birthplace of the revolt, SOHR said a man was shot dead at a checkpoint in an area where security forces were raiding towns after a soldier was killed at a checkpoint. Three other soldiers were killed in a rebel attack in the northeastern province of Hasaka, it said.

Independent verification of the reports is impossible because the Syrian authorities have barred access to foreign journalists and human rights workers.

Activists in the towns of Douma, near the capital Damascus, reported hearing explosions from heavy fighting overnight as ambulances raced through the city. By late morning they said the fighting had eased and reported seeing armored vehicles and snipers deployed through the city.

Army forces were also bombarding the town Qalaat al-Madyaq, close to Hama, with heavy artillery and mortar fire. They have been trying to storm the city for two weeks, the SOHR said, but have met stubborn resistance from rebel forces.

More than 8,000 people have died in the uprising, according to UN figures. Western and Arab states have accused the Syrian army of committing brutal abuses on unarmed civilians and have demanded that the autocratic Assad stand down.

The Syrian government says rebels have killed some 3,000 security forces and blames the violence on "terrorist" gangs.