Meanwhile, a watchdog reported that women and children were among 11 people killed in regime air raids and artillery fire on the town of Taftanaz, in the northwestern province of Idlib.
The Damascus blast hit near a research and testing centre affiliated with the ministry of industry in the Sumaria neighbourhood of the capital, state news agency SANA yesterday reported.
"A terrorist car bomb attack killed four people and wounded six others," SANA said, adding that the blast damaged shops and cars nearby.
Since the beginning of the conflict in March 2011, a series of car bombs have targeted Damascus, killing dozens.
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The Syrian Observatory for Human Rights said two women and three children were among 11 people killed in Taftanaz, where insurgents seized a military airbase in January after a long and fierce assault.
Taftanaz is located southwest of the northern city of Aleppo, and the Britain-based Observatory said the town was hit by at least three air raids during the day.
The watchdog also reported air raids on rebel positions in other parts of the country as well as clashes between regime forces and fighters near Damascus.
Regime forces also carried air raids over the town of Sabina, south of Damascus, while rebels fired rockets into the capital, it added.
Clashes also raged between rebels and troops in Moadamiyet al-Sham -- one of the sites allegedly hit by chemical attacks on August 21 -- and regime forces also bombarded Daraya, another town southwest of Damascus, it said.
The army has been unsuccessfully trying for months to take Moadamiyet al-Sham and Daraya back from the rebels.
The army also fired mortar rounds into the Yarmuk Palestinian refugee camp in southern Damascus, it added.