BEIRUT: An armed group in northwest Syria on Thursday hijacked a bus and kidnapped at least 40 civilians, mostly women and children, the Syrian Observatory for Human Rights said.

"Most of the victims were women and children, barring a couple of men," said Observatory director Rami Abdel Rahman, whose Britain-based centre added they came from Al-Fua and Kafraya villages in Idlib province.

Both are majority Shiite Muslim villages, while most rebels are Sunni.

The Observatory said the bus had been en route to Damascus. It did not specify which group was behind the kidnapping.

"The group were probably warlords who have taken advantage of a total security vacuum in areas where the army has pulled out," said Abdel Rahman, who warned that there has been an increase in kidnappings in northern Syria.

"There are many who are taking advantage of the conflict and an absence of centralised power," he said.

"We are very concerned about what may happen to these women and children."