"The Sham Front dug tunnels that reached the regime’s base located near Aleppo’s historical castle, and planted several mines and explosives in four buildings, which killed 15 of the Syrian regime’s soldiers," Sham Front spokesman Saleh Anadani said.
Several soldiers were also wounded in the explosions, Anadani added.
The clashes between regime forces and opposition groups took place in the old Aleppo area near the Umayyad Mosque, the spokesperson said.
The recent Sham Front is a unification of several opposition armed groups, including The Islamic Front that agreed to unite on Oct. 25.
Opposition forces in March 2011 began protests to topple President Assad, a struggle that turned into a civil war in July of that year after regime forces violently suppressed the demonstrations.