IS militia collapse following Syrian regime offensive in Yarmouk Valley

Syrian regime forces are laying siege to the last villages under the control of an Islamic State group affiliated militia - known as Jaish Khalid bin al-Waleed - in southern Syria, following a lightning campaign against the militants.

Syria's elite Tiger Forces, the Hizballah-linked Special Force, and Fourth Armoured Division - backed by Russian airpower - have led the offensive on the IS enclave in the Yarmouk Valley basin in Daraa province.

Around four or five villages remain in the hands of IS, according to Aymenn al-Tamimi, a researcher on Syrian militias, but it appears they too will soon fall to the regime

"[The campaign's success is] probably because of the overwhelming firepower and manpower advantage of the Syrian government, [and] also the intense Russian air raids," Tamimi told The New Arab.

"A number of ex-rebels have joined the fight on the government side."

Under cover of a massive artillery bombardment, regime forces entered the town of al-Shajara on Monday, described as the group's "main bastion".

Around 260 IS fighters have been killed since the regime launched an offensive on the territories in mid-July. 

It is not clear how many civilians have died amid the barrage of rockets and bombs hitting the Yarmouk Valley area, but images of recently recaptured towns and villages indicate the death toll could be high.

Read also: Yarmouk Martyrs Brigade/Jaish Khalid bin al-Waleed profile

Syrian state news agency SANA reported the death of al-Shajara's commander Abu Walid al-Masri during clashes on Monday. The fate of Jaish Khalid bin al-Waleed's other leaders remains unknown.
 
IS have hit back at the regime with suicide bomb attacks and explosives, in an attempt to slow the pace of the assault but with little effect.

Jaish Khalid bin al-Waleed previously operated in the area under the name the Yarmouk Martyrs' Brigade. 

The largely tribal outfit went to war with local rebel groups in Daraa province, following rumours that its leadership had sworn allegiance to IS head Abu Bakr al-Baghdadi.

Rebel campaigns against Jaish Khalid bin al-Waleed failed to dislodge the group from the valley. 

A huge regime offensive on opposition areas of Daraa province and Quneitra saw the collapse of rebel resistance in the area, leaving the Yarmouk Valley as one of the last areas on southern Syrian not under government control.

Faced with huge Russian bombing, many rebel groups agreed to surrender deals that required them to join regime security forces.

A number of former rebel groups, including the Youth of Sunna Forces, have taken part in the regime offensive on the Yarmouk Valley.