"Militants dug several tunnels under and around the Carlton hotel in Aleppo's Old City, where government troops are positioned. They used mines to detonate it this morning," claimed the Syrian Observatory for Human Rights.

"At least 18 others wounded in the attack, which also damaged parts of the hotel," the monitoring group added.

Fierce battles broke out after the attack, killing an unknown number of foreign backed militants.

Insurgents fighting to topple President Bashar Assad's government have used this tactic before, both in Aleppo, Syria's onetime commercial capital, and in Damascus province.

On another front, fresh infighting broke out between terrorist group of Islamic State of Iraq and Greater Syria (ISIS) and other militant groups.

On Friday, the militants drove out ISIS from their positions in five Aleppo provincial towns, including Hreitan, said the Observatory.

But just before their withdrawal from Hreitan, ISIS's fighters executed 13 civilians "who had links with other militants and who had been kidnapped."

Elsewhere, a car bomb attack killed 18 people in front of a mosque in rebel-held Yaduda village in the southern province of Daraa, said the Observatory.

More than 136,000 people have been killed in Syria's brutal war since March 2011, and millions more have fled their homes.

NJF/NJF