Syria is committing crimes against humanity as part of state policy to exact revenge against communities suspected of supporting rebels, Amnesty International said in a report.

The London-based rights group called for an international response after claiming it had fresh evidence that victims, including children, had been dragged from their homes and shot dead by soldiers, who in some cases then set the remains on fire.

"This disturbing new evidence of an organized pattern of grave abuses highlights the pressing need for decisive international action," said Amnesty's Donatella Rovera on release of the 70-page report entitled Deadly Reprisals.

The charity interviewed people in 23 towns and villages across Syria and concluded that Syrian government forces and militias were guilty of "grave human rights violations and serious violations of international humanitarian law amounting to crimes against humanity and war crimes."

Reporting on the revolt which broke out in March last year, Amnesty described how soldiers and shabiha militias burned down homes and properties and fired indiscriminately into residential areas, killing and injuring civilian bystanders.

"Everywhere I went, I met distraught residents who asked why the world is standing by and doing nothing," said Rovera.

The report also accused the regime of routinely torturing those who were arrested, including the sick and elderly.

In the report, Amnesty called on the United Nations Security Council to refer the case to the Prosecutor of the International Criminal Court (ICC), and to impose an arms embargo on Syria.

According to the Britain-based Syrian Observatory for Human Rights, more than 12,000 people have been killed since the uprising against President Bashar al-Assad began, most of them civilians.

Nine civilians and two rebels were killed early Thursday in violence across Syria, while car bombs exploded in the northwest city of Idlib and the capital Damascus, monitors reported.

The car bomb in Idlib city targeted a military checkpoint, the Syrian Observatory for Human Rights said, adding that a number of soldiers were killed or wounded in the blast. No further details were immediately available.

In Damascus, a car bomb exploded early morning in a suburb that houses a popular Shiite shrine, wounding two people, Syrian state media reported.

The blast in the Sayyida Zeinab neighbourhood occurred near the Sadr hospital, leaving a large crater and damaging vehicles.

State news agency SANA said the booby-trapped vehicle was parked in a garage. It gave an initial toll of two people wounded.

The Observatory said meanwhile that clashes between regime troops and rebels erupted early morning in the central city of Homs, where four people were killed before dawn, including three civilians and a rebel fighter.

It added that Ahmed Bahbouh, the head of the rebel military office in Rastan and a leading dissident figure, was killed in violent clashes with government forces in Homs province, the watchdog said.

A civilian was killed in crossfire as rebel fighters and government troops clashed at the entrances of the rebel-held town, which the regime has been trying to overrun for months.

In the southern city of Daraa five people were killed before dawn, including four in the neighbourhood of Tareek Al-Sad, which was heavily shelled by regime troops, the Observatory said.

"Government forces have surrounded the neighbourhood of Tareek Al-Sad in preparation to storm the area", it said.