Amman // A fragile truce was holding on Syria’s southern front on Tuesday after Jabhat Al Nusra killed a senior commander in a western-backed rebel group, accusing his faction of being sleeper agents for ISIL.

Mousab Ali Qarfan, who also went by the name Mousab Zaytouneh, was a leading figure in the powerful Shuhada Al Yarmouk Brigades. He was killed by the Al Qaeda-affiliated Nusra in Sahem El Golan, along with three other fighters from his group, on Monday.

The Yarmouk Brigades are part of the western-affiliated rebel alliance, still commonly referred to as the Free Syrian Army (FSA), which have been supported by the Military Operations Command (MOC) in Amman.

According to opposition sources monitoring Al Nusra, and information published on social media by activists close to the Al Qaeda affiliate, senior Al Nusra commanders believed Zaytouneh was secretly in league with the extremist militant group ISIL.

The Yarmouk Brigades are headed by Mohammad Al Baridi, known as Al Khal. They operate in southern Syria, including suburbs of Damascus. The unit headed by Zaytouneh operates in the south-west region of Deraa province, near the borders with Jordan and Israel.

There have been persistent rumours in rebel circles that various FSA brigades have secretly aligned themselves with ISIL, although none have been publicly named.

Moderate rebel commanders on the southern front denied the allegations about Al Khal, some saying the killing was part of an effort by Al Nusra to weaken a strong moderate rebel front.

Others said the claims of an ISIL connection were part of a psychological warfare programme by forces loyal to President Bashar Al Assad, seeking to divide and weaken rebels as they make steady advances in the south.

Rebel commanders and activists in southern Syria said the situation was tense on Tuesday night, with fears moderate factions and Nusra were on the brink of war, fracturing what has been one of the most coherent fronts against Assad forces.

The House of Justice, a court set up with backing by both the FSA and Nusra, has managed to broker a temporary truce between the groups over the killing.

However, its likely effectiveness appears dubious after Nusra and another Islamic faction, Harakat Al Muthana, withdrew from the court – effectively collapsing the unified justice system they had so recently established – leaving only FSA-appointed judges.

Nonetheless, the House of Justice yesterday proposed an armed force of moderate rebels should act as a buffer zone between the Yarmouk Brigades and Nusra to prevent more violence, until the killing can be investigated by the court.

As part of that proposal, Al Nusra has been told to pull back from a checkpoint it currently controls. If it fails to do so, moderates backed by the House of Justice say they will force the Al Qaeda affiliate to move.

Events leading up to Zaytouneh’s death remain murky, although the raid appears to have been sparked after the Yarmouk Brigades detained of several Al Nusra members, including the wife of an Al Nusra fighter on Sunday, who were accused of being part of an assassination squad attempting to murder Zaytouneh.

Al Nusra demanded the detainees be freed. When the Yarmouk Brigades refused, Al Nusra and Harakat Al Muthana jointly launched the attack in which Zaytouneh was killed.

Intermittent clashes between Al Nusra and the Yarmouk Brigades had taken place around Sahem El Golan in recent days, according to the Syrian Observatory for Human Rights a group monitoring the conflict.

Sources involved with the House of Justice said those took place as Abu Maria Al Qahtani, an Iraqi and a senior figure in Al Nusra, demanded he be allowed to arrest and punish the Yarmouk Brigades commander Al Khal, and another of its senior officers, Qahtan Bani Yarrob.

Deraa Governorate Council, aligned with moderate rebel factions, urged Al Nusra and the Yarmouk Brigades to honour the ceasefire.

“We call on the brothers in Liwa Shuhada Al Yarmouk and the brothers in Jabhat Al Nusra to exercise self restraint and to refer their case to the court in Houran, in the House of Justice to achieve justice,” a statement released by the council said.

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