At least 150 Syrian regime forces died in fighting with rebels for control of Khan al-Assal, a key town in the northern Aleppo province, the Syrian Observatory for Human Rights said on Friday.

It said more than 50 of those killed were executed by rebels after Khan al-Assal fell on Monday, while the rest died fighting for the regime's last bastion in the west of Aleppo province.

"Videos show what appears to be the collective execution of a number of soldiers," the opposition statement said.

"The Coalition condemns this act, and announces the creation of a commission of inquiry, stressing the need to take proceedings against those whose implication in the crime is proven."