Nine of the dead were members of the Islamic State, a group linked to Al Qaeda, while the rest were combatants from other Islamist groups such as the Al Nusra Front and the Syrian Islamic Front. (Agencies)
Criticism of the Islamic State for its behaviour on the ground and its radical interpretation of Islam have recently been raised by the opposition Islamist groups.
An Interior Ministry official said that seven of the fighters were executed by members of the Islamic State after besieging the building where the victims were holed up in northern province of Idleb.
In addition, fighting has been occurring in the provinces of Aleppo, Al Raqa and Hama.
The Islamic State has demanded the cessation of attacks against its non-Syrian fighters, the abolishment of checkpoints that hinder the movements of its members and the release of its fighters currently being held by other groups.
The conflicts within the forces opposing Syrian President Bashar Al Assad began last June when the Al Nusra Front, which is also linked to Al Qaeda, was designated by the terrorist group's leader, Ayman Al Zawahiri, as the only faction of his group in Syria and he asked the Islamic State to limit its activities in Iraq.
That decision provoked tension between the two groups which has been increasing in recent months.
More than 100,000 people have been killed since the start of the Syrian internal conflict in March 2011.
Nine of the dead were members of the Islamic State, a group linked to Al Qaeda, while the rest were combatants from other Islamist groups such as the Al Nusra Front and the Syrian Islamic Front.