"Three generals and a brigadier-general were among 31 troops killed in a bomb attack that caused a building in the army transport base in Harasta to collapse," said Syrian Observatory for Human Rights director Rami Abdel Rahman.
"The timing of the attack is significant," as it comes amid a major regime offensive on rebel positions all around Damascus, Abdel Rahman told AFP.
The bomb appeared to have been placed "either inside or beneath the building in a tunnel", he added, suggesting there was a possibility rebels had infiltrated the base.