Syrian rebels blow up tunnel in Aleppo, killing at least 20 government fighters

Syrian activists say rebels have blown up a tunnel packed with explosives in the northern city of Aleppo, killing at least 20 pro-government fighters.

The Britain-based Syrian Observatory for Human Rights says the blast took place Friday near the Zahrawi market not far from the citadel in Old Aleppo. It says clashes followed the explosion.

A powerful rebel alliance called the Islamic Front claimed responsibility for the blast. It said in a tweet that it killed at least 40 government gunmen.

The Islamic Front also tweeted a video of the explosion. It shows a massive blast erupting from a skyline of rooftops and satellite dishes, throwing chunks of brick and a huge cloud of dust into the air.

The video appeared genuine and corresponded to other Associated Press reporting.