Syrian rebels have claimed responsibility for the bombing of a hotel being used by the military in the northern city of Aleppo.
Reports say the explosion struck a government-held area on the edge of a contested neighbourhood in the Old City of Aleppo. The television report identified the hotel as the Carlton Citadel hotel.
The attack in Aleppo is a significant blow to president Bashar Assad's government in the north as his troops prepare to regain control of the central city of Homs following last week's ceasefire agreement after a fierce, two-year battle with the rebels trying to oust him.
No such agreement appears to be in sight in Aleppo, Syria's largest city and former commercial hub. The city has been carved up into opposition - and government-held areas since the rebels launched an offensive there in mid-2012, capturing territory along Syria's northern border with Turkey.
In recent months, government aircraft has bombed rebel-held areas of the city and the opposition fighters have hit back, firing mortars into government-held areas. The rebels have also detonated car bombs in residential areas, killing dozens of people.
The hotel attack targeted a government-held area on the edge of a contested neighbourhood in Aleppo. Reports say terrorists - a term the government uses for rebels - dug up tunnels under Aleppo's ancient district and detonated explosives there.
A local activist group called the Sham News Network also reported the blast, saying that Assad's troops were based in the hotel.
The Islamic Front rebel group claimed responsibility for the blast. A statement posted on its official Twitter account on Thursday said that its "fighters this morning levelled the Carlton Hotel barracks in Old Aleppo and a number of buildings near it, killing 50 soldiers". It did not say how it knew how many soldiers died.
The Islamic Front is an alliance of several Islamic groups fighting to topple Assad. Many of its fighters have joined the Front after breaking away from the Western-backed Syrian Free Army last year.
Another activist group, the Britain-based Syrian Observatory for Human Rights, said Islamic Front fighters planted a huge amount of explosives in a tunnel they dug below the hotel and detonated it remotely.
It said the hotel was completely destroyed in the blast and that there were casualties among the troops.