Activists say members of al-Qaida's affiliate in Syria have shot dead at least 45 soldiers captured alive from a base in northwestern Syria last week.

The Britain-based Syrian Observatory for Human Rights said on Saturday that 56 soldiers were killed in the Abu Zuhour air base that was captured by the Nusra Front and other militant groups on Sept. 9.

Mohammed Kanaan, an activist based in Syria, said the Nusra Front shot dead 45 soldiers adding that the "executions" took place on a runway in the air base. He said the killings occurred Friday.

The capture of Abu Zuhour air base was the latest in a series of setbacks for President Bashar Assad in Syria's bitter civil war, now in its fifth year.