Beirut: Insurgents attacked a Syrian government security building in the northern city of Aleppo on Wednesday, setting off a bomb and then launching a ground assault. A monitoring group said dozens were killed on both sides.
The Syrian Observatory for Human Rights, which monitors the war using sources on the ground, said the attack on the Air Force Intelligence building was carried out by jihadist groups including the al Qaeda-linked Nusra Front.
Initial reports suggested the insurgents had set off the bomb in a tunnel dug under or near the building in Aleppo, which has long been a focus of fighting between government and insurgent groups.
Rebel sources and a combatant fighting on the government side confirmed that part of the building had been destroyed in the attack on the western outskirts of Aleppo.
Air Force Intelligence is widely viewed as one of the most powerful arms of the Syrian security establishment.
In a statement circulated by Nusra Front supporters on Twitter, the group said "the Mujahideen destroyed Air Force intelligence" and were fighting in the surrounding areas.
Rami Abdulrahman, who runs the Observatory, described it as a blow to the Syrian security establishment. "It`s very important, it should have been better protected," he said.
Abdulrahman said the dead included members of the Syrian intelligence apparatus, pro-government fighters, and some of the attackers.
Aleppo, around 50 km (30 miles) south of the border with Turkey, is divided between government forces and insurgent groups fighting to topple President Bashar al-Assad in a four-year-old conflict estimated to have killed 200,000 people.
U.N. envoy Staffan de Mistura is currently trying to broker a ceasefire between insurgent and government forces in Aleppo. His team headed there on Tuesday.
Government forces backed by allied militia launched a major offensive aiming to encircle the insurgent-held part of Aleppo late last month, but the offensive was repulsed.