Amman // Rebels in southern Syria have renewed a faltering advance against ISIL factions amid hopes the US is positioning itself to carry out air strikes in the contested border zone near Jordan and Israel.

Backed by their Western allies and benefactors in the Arabian Gulf, the rebels began a campaign in March against the Yarmouk Martyrs Brigade and Harakat Al Muthanna, two factions affiliated with ISIL. The effort, timed to coincide with a fragile ceasefire between rebel and regime forces, has failed to make significant progress however. Last week, the Military Operations Command (MOC), a control centre in Amman staffed by military officials from western and Gulf states, suspended weapons shipments and payments intended for the anti-ISIL rebels, following through on a previous threat to withdraw support if rebels did not advance.

Rebels close to the MOC said they received a scheduled shipment of munitions this week but that no more will be supplied until progress is made against ISIL in western Deraa province.

In what appears to be a response to that freeze, on Monday rebels on the southern front announced a new assault against ISIL in the Yarmouk Basin area, near the border with Israel. They vowed to continue the attack until “all ISIL fighters were expelled”. Fighting subsequently erupted at Ain Zakr, with rebels reportedly taking control of an ISIL checkpoint.

Colonel Najim Abu Majid, the rebel commander tasked with overseeing the anti-ISIL effort in Deraa, was also replaced by Col Saber Sifir.

The renewed effort has been buoyed by Washington’s announcement last Thursday that it was classifying the Yarmouk Martyrs Brigade a Specially Designated Global Terrorist Threat. Jabhat Al Nusra, the Al Qaeda affiliate, and ISIL are both already on the list. The Yarmouk Martyrs Brigade shares ISIL’s ideology but has not publicly merged with it.

Under the classification, assets linked to the brigade have been blocked. More significantly, however, rebels hope the move may pave the way for US airstrikes and Washington’s first direct combat role in the skies over southern Syria.

“When the Americans declared them a terrorist organisation, it means they will directly target them [Yarmouk Martyrs Brigade], which also serves our interests because they are our enemy,” said Issam Al Rayes, a spokesman for the southern front rebel alliance.

Airstrikes have been critical in victories by the Syrian Democratic Forces, an alliance dominated by Kurdish militia units, in the north and east of Syria. With US air support they have been able to roll back areas under ISIL control. Small units of US special forces have also been deployed on the ground in the north.

In the south, however, rebels have not received any air support, just limited training and restricted arms supplies, leaving them to break through heavily fortified ISIL lines alone.

Another rebel commander said he now expected the US to mirror that northern Syria strategy in the south.

“Including the Yarmouk Martyrs Brigade on the terrorist list suggests that the anti-ISIL alliance could fight them in the same way they are fighting them in the north,” he said.

The US government has not said publicly whether airstrikes are in the pipeline and a US official familiar with Middle East policy downplayed the prospect, noting that regime air defences in the south, close to Damascus and Israel, were dramatically stronger than in the north.

Forces loyal to president Bashar Al Assad have long enjoyed a monopoly in the skies over southern Syria, using barrel bombs against military and civilian targets to hold back advancing rebels. Intensive Russian airstrikes were crucial during January’s rebel defeat at Sheikh Miskeen, a strategically important town between Deraa and Damascus.

Since 2012, rebels and some of their Western and Arab allies have called for no fly zones in northern and southern Syria. The US, reluctant to get embroiled in the conflict, vetoed the plan, in part because enforcement would require destroying air defence facilities. While unwilling to carry out air strikes against regime forces, however, the US may be willing to do so against ISIL factions.

Nicholas Heras, Middle East researcher at the Centre for a New American Security, said the global terrorism classification gave Washington the option of moving more forcefully into the war in southern Syria.

“The US could start conducting air strikes against the Yarmouk Martyrs Brigade, and in the process, create a de facto safe zone, or sphere of influence, in south-western Syria similar to the one that it has carved out of north-eastern Syria in support of the Syrian Democratic Forces (SDF),” he said.

He stressed that any US moves towards airstrikes were likely to be “gradual”.

American involvement against the Yarmouk Martyrs Brigade may prove essential if the group is to be defeated. Rebels have been unable to attack the group forcefully, in part because, unlike ISIL elsewhere in Syria, most of its fighters are local, and it has strong ties to the areas it controls in western Deraa. There are also foreign militants, including Saudis and Afghans, in the group, which rebels say number between 450 and 600 fighters.

“YMB fighters come from the same area and therefore they have a popular base. It is difficult to have fighters from other areas fighting there, especially given that [local] people de not welcome the [MOC] rebels,” said Issam Al Rayes, the southern front spokesman.

The Yarmouk Martyrs Brigade and Harakat Al Muthanna have also carried out an effective campaign of assassinations against rebels who dare to oppose them, killing scores of fighters and commanders.

In an attempt to break the reluctance to attack ISIL factions in the south, rebels say the MOC has offered a US$100,000 (Dh367,295) cash payment to any faction that does fully engage in the assault.

Another reason rebel field commanders say they have been unable to make rapid gains is a lack of weapons. Although supplied by the MOC, weapon flows are tightly controlled, and commanders complain they frequently run short of munitions. Resupplies come too slowly, they say, forcing them to look to arms traders for bullets, missiles and mortars.

“Military assistance to the MOC-backed groups could flow more fully [after the global terrorism classification],” Mr Heras said.

The US has made clear it’s alarm about the rising influence of ISIL in the south, and the threat that this poses to its’ regional allies, including Jordan.

During a visit to Amman in May, Brett McGurk, president Barack Obama’s envoy to the US-led coalition fighting ISIL, said Washington was working with moderate rebels to “fight pockets” of ISIL in southern Syria, as well as in the north of the country.

“As we began to put pressure from the north we are going to make sure that Daesh [ISIL] cannot shift its forces south, particularly here in Jordan, and of course we are working very closely with the moderate opposition,” he told a press conference at the time.

Harakat Al Muthanna and the Yarmouk Martyrs Brigade, announced a merger last month, joining together as the Khalid Bin Walid Army. Fighters from the Jaish Al Jihad, led by Abu Musab Al Fannousi, also joined. The move appears to have been in response to the campaign against them by moderate rebel factions.

foreign.desk@thenational.ae