Rebels attacked a convoy of trucks and buses in northern Syria, activists said on Wednesday, after Islamist militants had warned they would target all vehicles on the road to stop the army from using its only remaining route to Aleppo.
One woman was killed and 19 people were wounded, some critically, according to the Syrian Observatory for Human Rights, an anti-Assad monitoring group based in Britain.
The hardline Islamist rebel group Ahrar al-Sham uploaded video footage of the attack onto YouTube on Tuesday. It shows rebels firing artillery and mortars from a barren hillside and several trucks on fire. There is no return fire from the convoy of around 30 vehicles on the road between Salamiyeh, east of the central city of Homs, and Aleppo, Syria's largest city.
The Syrian conflict started with peaceful protests in March 2011, but after a crackdown by government forces turned into a civil war that has become increasingly sectarian. Nearly 100,000 people have been killed, according to the United Nations.
Majority Sunni Muslims lead the revolt, while Assad, whose family has ruled Syria for 43 years, gets his core support from his own Alawite sect, an offshoot of Shi'ite Islam.
"We warn civilians against being dragged into the criminal regime's attempts to use them as human shields and as a cover to secure its movements," the statement said.
An unidentified voice in Tuesday's video says the attack hit a military convoy. Activists said the victims were civilians.
"They are all Christian Syrian-Armenians who live in Aleppo. They travelled in a large convoy because it is safer," said Abdelrahman, citing medical staff at an Aleppo hospital where the wounded were being treated.
Pulse Gathering for Syrian Civil Youth, which calls itself a non-violent group against sectarianism, said on its Facebook page on Wednesday that the attack targeted civilians, including women and children, and called it "a reprehensible crime".
Syrian state media have not mentioned the incident.
Reporting and security restrictions make it hard to verify accounts of events in Syria.