A video, which was released on the Internet on Sunday, shows the Syrian insurgents cheering after the explosion.
Some media sources have accused the Syrian government of the bombing.
Earlier in the day, two other videos were released online, one showing members of the FSA, equipped with US-made weapons.
Syria has been experiencing unrest since March 2011. Damascus says the turmoil, which has killed many people, including large numbers of security forces, is being orchestrated from outside the country.
There are reports that a very large number of the insurgents are foreign nationals. Damascus has repeatedly criticized the United States and its regional allies, including Saudi Arabia, Qatar, and Turkey, over funding and arming insurgents fighting the government forces.