"Setting up car bombs in the capital or anywhere in the country is not a strategy that the FSA condones," Almokdad said. "We reject targeting any civilian area and risking the lives of our civilian population."
Tuesday's blast occurred a day after Syrian Prime Minister Wael al-Halqi survived a bombing that targeted his motorcade in an upscale Damascus neighborhood, the government and opposition reported.
The Syrian Observatory said one of al-Halqi's escorts and five civilians were killed in the explosion. Another escort and a driver were badly injured, the group said.
The state-run Syrian Arab News Agency reported casualties but did not elaborate on the incident.
No one immediately claimed responsibility for the Monday blast. But the rebel spokesman said he believes that attack was also set up by the government.
"Al-Halqi is a minor figure propped by the al-Assad regime, and he is not a strategic target to the FSA or anyone in the revolution. We actually feel sorry for the man who was appointed to be a prime minister," he said.
The Syrian civil war has pitted al-Assad's forces against rebels seeking an end to four decades of Assad family rule.
More than 70,000 people, mostly civilians, have been killed in the conflict in the past two years.