At least 13 pro-government troops were killed in Syria on Tuesday when opposition fighters detonated explosives in two tunnels under the old police headquarters in Aleppo, the Syrian Observatory for Human Rights (SOHR) said.
Following the blasts, clashes erupted between the regime troops and the opposition Islamic groups, and are still on.
Today's attack is one in a series of blasts of tunnels carried out by the opposition in the old part of Aleppo.