Syrian rebels execute youths
Al-Qaida linked rebels fighting Assad execute two Shiite young men in Aleppo - YouTube screen grab

A chilling video of Syrian Islamist rebels linked to al-Qaida executing two young men has surfaced online.

The militant group reportedly executed the two for supporting President Bashar al-Assad's regime.

The executions are believed to have taken place in a village in the northern Syrian province of Aleppo. The Shiite-community boys were said to be from Nubul and Zahra towns.

The incident has been confirmed by the Britain-based monitoring group, Syrian Observatory for Human Rights, which largely opposes Assad's regime. The group said Assad refused to swap rebel prisoners for the boys leading to the execution.

In the video, the men are seen blindfolded and kneeling before a masked rebel fighter. The fighter reads a statement in the name of the Islamic State of Iraq and the Levant, said to be a frontline rebel group in Syria.

"It is our duty to execute them," says the fighter and as he walks away, the militants open fire at the men bellowing "Allah Akbar" or "God is great".

The executions are yet another illustration of what is seen as a paradigm shift taking place in strife-torn Syria. The uprising-turned-civil war has been snowballing into a sectarian conflict as Sunni insurgents fight against Assad's Alawaite minority.