Syrian security forces have shot dead up to four civilians travelling in a bus at a government road block in the northern province of Idlib, rights groups have told the Reuters news agency.

Amateur video footage posted on the Internet showed the bodies of two women, an unconscious man and a man who appeared to be bleeding from his head and his abdomen.

"This is from the regime of [President] Bashar al-Assad," the man holding the camera said.

"Four citizens on a bus were killed after being shot at a security checkpoint near Khan Sheikhoun," the British-based
Syrian Observatory for Human Rights said.

The grassroots Local Co-ordination Committees said three people were killed and four others were severely wounded when security forces fired on the bus on the highway, which links Aleppo with Damascus.