Two Syrian activist groups say about 5,000 people were killed in Syria in August, making it the deadliest month since the uprising began more than 17 months ago.

The Britain-based Syrian Observatory for Human Rights said Sunday that 5,440 people, including 4,114 civilians were killed.

Meanwhile the Local Co-ordination Committees, another activist group, said 4,933 civilians were killed in August.

The civil war witnessed a major turning point in August when President Bashar al-Assad's forces began widely using air power for the first time to crush the revolt.

The fighting also reached Syria's largest city, Aleppo, which had been relatively quiet for most of the revolt.

The UN children's fund UNICEF came out with its own estimate on Sunday, saying at least 1,600 people were killed last week in Syria in the deadliest seven days since the uprising against Assad began in March 2011.

While the military largely has been able to quell the offensive rebels launched in Damascus in July, it is still struggling to stamp out a rebel push in the northern city of Aleppo.

Fighting rages in several areas

In the latest violence on Sunday, the Observatory said the military pounded rebel holdouts in Aleppo, the country's commercial capital. There was also fighting in central city of Homs, Idlib province on the border of Turkey and suburbs near Damascus.

The Observatory said several people were killed in the violence, but did not have any figures.

Smoke rises from the site of an explosion in central Damascus on Sunday. Smoke rises from the site of an explosion in central Damascus on Sunday. (Twitter)

Two bombs exploded near the Syrian military's joint chiefs of staff offices in central Damascus, lightly wounding four army officers and damaging buildings and cars, state television reported. The twin blasts in the posh Abu Rummaneh district were the latest in a wave of bombings to hit Damascus in recent months as clashes between government troops and rebels reached the tightly controlled capital.

There was no immediate claim of responsibility for the bombings, which government officials said appeared to target a building under construction near the offices of the joint chiefs of staff. The building, which is officially known as the Guards Battalion and was empty at the time of the blast, serves as a base for army officers who guard the joint chiefs of staff offices some 200 metres (yards) away.

Several past bombings have targeted the security establishment in Damascus, most notably a July blast that killed four senior security officials, including the defence minister and his deputy, who was Assad's brother-in-law.

Syrian officers injured in attack

The government officials, speaking on condition of anonymity because they are not authorized to brief the media, said the wounded Sunday were army officers and they had minor injuries.

Footage broadcast on state TV showed a damaged building with debris strewn across the street. The blasts punched a hole in one of the building's walls, and blew out the windshield and windows of an SUV parked nearby.

The twin bombing was the second in recent weeks to hit Abu Rummaneh. On Aug. 15, a bomb attached to a fuel truck exploded outside the Dama Rose hotel where UN observers stayed before ending their mission to Syria. That blast, which hit a military compound parking lot, wounded three people.

Late Saturday, a car bomb near a Palestinian refugee camp in a suburb of Damascus killed at least 15 people, according to state news agency SANA. It said Sunday the explosion in the suburb of al-Sbeineh also wounded several people and caused heavy damage to buildings in the area.

It blamed the blast on an "armed terrorist group," the term the regime uses to describe the rebel Free Syrian Army seeking to topple Assad.

When Syria's unrest began, the country's half-million Palestinians at first struggled to remain on the sidelines. But in the past months, young Palestinian refugees — enraged by mounting violence and moved by Arab Spring calls for greater freedoms — have been taking to the streets and even joining the rebels.