Aleppo, Syria
Aleppo, SyriaReuters File

Almost 40 Syrian soldiers and pro-regime fighters were killed on Friday when rebels blew up a tunnel that was under a government position in Aleppo, Syria.

At least 38 members of the government forces died after a building used by the regime in the Old City of Aleppo was blown up on Thursday, the Syrian Observatory for Human Rights, which is based in Britain, said.

The Thuwwar al-Sham rebel group posted a video online which showed members of the force soldiers walking through a long tunnel and preparing barrels full of explosives.

"We are now inside the tunnel that will be detonated soon, God willing, the tunnel under the traffic branch building, which is an important headquarters for the Assad regime and its mercenaries," a rebel said in the video, according to a report by AFP.

The footage then showed a huge blast levelling a multi-story building, filmed from different angles. A huge geyser of dirt and smoke shot upwards from the scene of the blast following which gunshots could be heard.

Aleppo, once Syria's financial capital, has been ravaged by conflict that began in 2011. It has been divided between government control in the west and rebel control, which has been under siege since a couple of weeks, in the east.