BEIRUT, Lebanon — A hotel used by Syrian government troops in the northern city of Aleppo was leveled by a huge explosion Thursday after Islamic militants tunneled underneath the building and planted explosives linked to remote detonators, activist groups and state media reported.
There was no immediate word on casualties. Video footage, whose authenticity could not immediately be confirmed, showed huge clouds of gray smoke blotting out the Aleppo skyline.
The Islamic Front, one of the biggest insurgent groups in Syria, claimed responsibility for the blast, saying the attack was a response to the mass killing of unarmed civilians in Aleppo.
The group, a coalition of insurgents including former Free Syrian Army fighters and members of harder-core Islamist factions, said the attack was a prelude to a "large-scale operation" meant to secure territorial gains.
The state news agency, SANA, said the attack had rocked the Old City area of Aleppo and destroyed historical sites there. The attackers blew up tunnels they dug under archaeological buildings, SANA said.
State television identified the destroyed hotel as the Carlton, which was built as a hospital in the era of Ottoman rule before World War I and later renovated and reopened as a hotel, facing the historic citadel in Aleppo. Government forces had been billeted there for two years.
The Syrian Observatory for Human Rights, an opposition group that is based in Britain and collects information from contacts inside Syria, said Islamist forces had tunneled under the hotel from areas held by rebels seeking the overthrow of President Bashar Assad.
An activist group, the Shaam News Network, said government forces had been based in the hotel.
Aleppo, the country's largest city, has been carved into a checkerboard of areas held by one side or the other as the Syrian civil war has intensified. Government forces have been bombing rebel areas from the air, while the rebels have detonated car bombs and fired mortar rounds into government-held districts.