Updated

Syrian activists say al-Qaida militants in northern Syria have killed two young Shiite men execution style.

The Britain-based Syrian Observatory for Human Rights says the men, who were shot in the head, came from the besieged Shiite-majority towns of Nubul and Zahra in Aleppo province.

Syria's conflict has taken on an increasingly sectarian tone over the last year, pitting predominantly Sunni Muslim rebels against members of Assad's Alawite sect, an offshoot of Shiite Islam.

An amateur video posted online showed two blindfolded men sitting before a masked gunman before they were shot.

The videos appeared genuine and corresponded to other AP reporting on the events depicted.

Unrest in Syria began in March 2011 and later exploded into a civil war. More than 100,000 people have been killed in the conflict.