An Egyptian court has sentenced three Syrian nationals to death over the murder of a fellow citizen in Cairo for his alleged support to President Bashar Al-Assad in Syria's civil war, a judicial source has said.

The charges stem from August 2013 when a Syrian student was killed in an eastern Cairo apartment by three of his fellow countryman to avenge his alleged killing of six of Assad's opponents before fleeing to Cairo.

The sentences were ratified by the Egypt's Grand Mufti, or top Muslim cleric, who according to Egyptian law should review all death sentences.

The ruling can still be appealed before the Court of Cassation, Egypt's highest judicial authority.

Syria has faced four years of armed revolt, after President Bashar Al-Assad refused to step down following peaceful demonstrations against four decades of rule by his family in early 2011.

Human rights groups say that over 200,000 people have been killed in the fighting.

The lingering fighting between Al-Assad's government and non-Islamist rebels has recently been eclipsed by the government and allied militia's war against the Islamic State (IS) militant group, which has seized swathes of territory in Syria and Iraq.