Video of rebel forces in Aleppo digging a tunnel and exploding a fertilizer bomb under the Carlton Citadel Hotel

A "huge explosion" in northern Syria leveled a hotel that government troops used as a military base, along with several other buildings in a government-held area, state television and activists reported on Thursday. Footage has emerged purporting to show the moment of the blast which sent up a huge plume of smoke. Syrian state television said the explosion struck on the edge of a contested old neighborhood in Aleppo. The television report identified the hotel as the Carlton hotel. A local activist group called the Sham News Network also reported the blast, saying that President Bashar al-Assad's troops were based in the hotel. Another activist group, the Britain-based Syrian Observatory for Human Rights, said the explosion struck Aleppo's Old City, where rebels have been holed up from months. The Observatory said the rebels belonging to the Islamic Front group planted a huge amount of explosives in a tunnel they dug below the Charlton hotel, detonating it remotely. It said the hotel was completely destroyed in the blast and that there were casualties among the troops. Aleppo, the country's largest city and former commercial hub, is carved up into rebel-held and government-held areas since the rebels launched an offensive there in mid-2010, capturing territory along Syria's northern border with Turkey. In recent months, government aircraft relentlessly has bombed rebel-held areas of the city and the opposition fighters have hit back, firing mortars into government-held areas. The rebels also have detonated car bombs in residential areas, killing dozens of people.