Armed extremist groups in Syria such as the al-Qaeda-inspired Islamic State of Iraq and the Levant (ISIL) and Jabhat al-Nusra (JAN) have been using murder and executions to intimidate people and impose their control in opposition-held areas, analysts said.

The Office of the UN High Commissioner for Human Rights (OHCHR) in January said it received reports of a series of mass executions of civilians and fighters who were no longer participating in hostilities by hard-line armed opposition groups in Syria, in particular the ISIL.

"While exact numbers are difficult to verify, reliable eyewitness testimony that we have gathered suggests that many civilians and fighters in the custody of extremist armed opposition groups have been executed since the beginning of this year," said UN High Commissioner for Human Rights Navi Pillay.

"The execution of civilians and individuals no longer participating in hostilities is a clear violation of international human rights and international humanitarian law and may constitute war crimes."

Reports suggest that in the first week of January, numerous individuals were executed in Idlib by armed opposition groups.

"Execution, per se, if carried out by a party that does not have the capacity to do so by law, amounts to a crime," said Cairo University international criminal law professor Wael al-Sharimi. "This applies to the case in Syria, wherein the warring parties, particularly ISIL and JAN, are carrying out physical elimination without any legal cover.

"It is also very clear that execution and murder in this manner cannot be classified as killing in the course of battle since many of the executions were carried out against unarmed civilians, and many others against fighters who had surrendered."

Al-Qaeda's MO

The modus operandi of al-Qaeda and its affiliates is murder, whether by public executions or suicide bombings, said military analyst and al-Qaeda affairs specialist Abdul Karim Ahmed.

"Therefore, it is not surprising that militants from such organisations execute in cold blood, anyone who opposes their views," he said.

In December 2013, ISIL fighters executed a mentally disabled Syrian fuel vendor in Saraqeb, sparking criticism of the group's misappropriation of Islam as a pretext for their crimes.

"What helps them implement this modus operandi is the militants' weak religious knowledge and their delusion of the need to carry out orders under the pretext of 'real' fatwas, i.e. fatwas issued in response to a specific and emergent event," Ahmed said.

ISIL and JAN use the same method to intimidate people, said Mahmoud Rafih, an activist with the local co-ordination committee in Manbij.

Contrary to Islamic tradition, corpses are not buried within 24 hours and instead are left out in full view for days. Rafih said this strikes horror in the hearts of citizens and combatants alike. Infighting and fragmentation

Al-Qaeda-linked groups that say they are trying to establish an Islamic state in Syria fight among themselves for control of Syria's economic resources, Ahmed, the military analyst, pointed out.

"What is happening in Syria clearly reveals two things: the first is how far removed al-Qaeda elements are from the Islamic slogans they pretend to promote," said Ahmed, "in particular the unity of Muslims and the predominance of the citizens' interest over any other, putting instead their personal interests above all and displaying their internal conflicts."

"The second is the fragmentation of al-Qaeda," he said.