Large explosion and heavy clashes in Aleppo

Britain-based Syrian Observatory for Human Rights said the blast hit a building housing the Air Force Intelligence offices in the west of Syria's second city and was followed by heavy clashes on Wednesday.

According to the Observatory and the Aleppo Media Center, at least 20 government troops and 14 militants were killed in the attack, which was led by the Nusra Front and other radical Islamic armed groups.

"The explosion and the fighting caused dozens of deaths on both sides," the Britain-based group said, adding that part of the building had collapsed.

A Syrian military source confirmed the explosion and said clashes were continuing. "Gunmen blew up a tunnel that they dug (into the regime-controlled sector) and then attacked the area surrounding the Air Force Intelligence headquarters," the source said.

Al-Nusra responsible for the attacks

Furthermore, Syrian al Qaeda affiliate al-Nusra Front also published on Twitter that its fighters, along with members of other rebel factions, were storming the Air Force Intelligence headquarters.

Government artillery and aircraft pounded rebel positions in the area in response, the Britain-based group said, while fighting also flared up around Aleppo's historic citadel in the heart of the badly damaged Old City.

A similar blast from explosives planted in a tunnel under Aleppo's Old City in December killed at least seven government troops.

Observers said that the fall of eastern Aleppo would be a critical blow to Syrian rebels, who are caught between resurgent government forces and the jihadists of Islamic State.

jil/lw (dpa, AFP, AP)