DAMASCUS, Syria—At least 150 Syrian soldiers were killed this week in a rebel attack that leveled the main buildings at a large base outside Damascus, one of the single highest death tolls of government troops since the start of the armed uprising, according to military and security personnel with knowledge of the assault.

A Syrian military spokesman confirmed earlier rebel accounts that they had tunneled under the buildings for months, then filled them with explosives and blew them up on Sunday.

...