DAMASCUS - Syrian rebels downed an army helicopter for the first time on Tuesday with a ground-to-air missile from newly acquired stocks, a watchdog said, in a potential turning point for the 20-month conflict.

A car bomb hit a regime security post near Damascus and clashes raged around the capital, as rebels further tightened the noose around the key northern city of Aleppo.

Human Rights Watch called on Syria’s army to stop using cluster bombs, two days after an air strike killed at least 11 children and state media published the names of nearly 150 foreign fighters it said had died alongside insurgents.

“It is the first time that the rebels have shot down a helicopter with a surface-to-air missile,” Syrian Observatory for Human Rights director Rami Abdel Rahman said of the gunship that was on a strafing run near a besieged northwest base.

The Sheikh Suleiman base, 25 km west of Aleppo, is the last garrison in government hands between Syria’s second city and the Turkish border.  The Observatory said the missile was part of a consignment newly received by the rebels that had the potential to change the balance of military power in the conflict which began as a peaceful uprising in March last year.

Near Damascus, a car bomb killed at least two soldiers at a military police checkpoint in Jdeidet Artuz as the regime pursued its efforts against insurgent strongholds south of the capital.

Battles raged in Moadamiyet al-Sham and nearby Daraya, where a massacre in August killed more than 500 people, according to the Observatory. Rebels meanwhile seized a military post 15 kilometres southeast of Aleppo, tightening the noose around the city, both the insurgents and the Observatory said. After hours of fighting, the rebels in the area said they had taken the post at dawn in the village of Al-Mintar, near Al-Safireh.

Elsewhere, in Idlib province in the northwest, an aerial bombardment near an olive press killed at least five people and wounded dozens, the Observatory said.

In the same province, rebel-held Maaret al-Numan was also bombed from the air as clashes raged at the southern entrance of the town strategically located on the Damascus-Aleppo road. Human Rights Watch called on the army to stop using cluster bombs after at least 11 children were killed by an air strike south of Damascus on Sunday.

An initial toll from the Observatory, which relies on a network of activists and medics for its information, said 87 people were killed across Syria on Tuesday, including 32 civilians. The watchdog has recorded a total of more than 40,000 deaths in the Syrian conflict.