Beirut:  Blasts rocked the flashpoint city of Homs on Sunday as Syria's regime pressed its assault on protest hubs, with another 31 people, including 16 civilians, killed in violence across the country, activists and monitors said.

There was "heavy shelling of Khaldiyah, Hamidiyah and Old Homs neighbourhoods by the regime's army, and explosions shook the whole city," the Local Coordination Committees said.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, said in a statement that four civilians were killed by security force fire in the Homs area.

Three, including an infant, died in Homs itself, while the fourth - a young girl - was killed in Rastan by heavy machinegun fire. The Observatory also said a member of the security forces was killed in Homs city.

In the central Hama region to the north, the monitoring group said army shelling killed five civilians in the Murk and Latamna districts.

And in the southern town of Nawa, tanks entered the main streets, and heavy clashes broke out between regime forces and deserters, said the Observatory and the LCC, the main opposition activist group in Syria. Three soldiers and eight rebel fighters were reportedly killed.

LCC activist Luai Rushod in Nawa spoke of "a large number of defections by soldiers in the southern part of Nawa, followed by clashes and troops committing barbaric murders."

Nawa is in the southern Daraa province, where the popular uprising against President Bashar Al Assad's iron-fisted rule erupted in March 2011. Monitors say at least 9,100 people have been killed since then.

The Observatory said an explosion hit a bridge in the Daraa region of Lajat, where many army deserters are thought to be.

In the north, near the border with Turkey, rockets were fired into the town of Aazaz as helicopters flew overhead, the LCC said in a statement sent to AFP in Beirut.

It added that rebel fighters of the Free Syrian Army blocked a highway used by the military for reinforcements and supplies to Aazaz, the scene of fierce clashes for the past few weeks.

Two deserters were killed in fighting in Aazaz with government forces using heavy machineguns and mortars, it said.

In the northwest province of Idlib, regime troops killed seven civilians, including three children, in the town of Saraqeb and in Kaframim village, where they torched the houses of dozens of fleeing rebels.

"Deserters have begun pulling out of Saraqeb," said the Observatory, which also reported fighting in the town of Ariha to the west.

Human Rights Watch on Sunday accused regime forces of using civilians as human shields to march in front of them as they advanced on opposition-controlled towns in Idlib.

"By using civilians as human shields, the Syrian army is showing blatant disregard for their safety," HRW emergencies researcher Ole Solvang said in a statement, urging the army to immediately halt "this abhorrent practice."

In Damascus province, rebels fired rocket-propelled grenades in a dawn attack on a military facility in Nabak, the Observatory said.

Mohammad Al Shami, an activist, said fighting erupted at night between soldiers and army deserters and continued into the early hours, including in Douma, a hot spot on the capital's northeastern outskirts, where a young man was killed, according to the Observatory.

Elsewhere, the official Sana news agency said that an "armed terrorist group" attacked a gas pipeline in the eastern region of Bir Al Jouf.

At least 28 civilians were killed across Syria on Saturday, including two women and two children in the central province of Homs, the Observatory said.

Sixteen soldiers and two deserters were also reportedly killed.

As the year-old conflict showed no signs of abating, rebel fighters set up a military council to unify their ranks and political opposition leaders called a meeting of all dissident groups to forge common objectives.

The latest violence came as UN-Arab League envoy Kofi Annan wrapped up and trip to Moscow to seek the vital backing of Russia, a key ally of the Syrian regime, for his plan to end the bloodshed.