AMMAN (Reuters) - Islamic State-linked Syrian militant groups on Monday launched a surprise attack on moderate rebels in southwestern Syria near the Golan Heights near where the Jordanian and Israeli borders converge, seizing several villages and a large town, rebels and witnesses said.

Rebels said the militants were able to extend their area of control in territory that forms a natural barrier between Syria and Israel where the Yarmouk River flows after they overran the towns of Tseel, Sahem al Golan, Adwan and Tel Jamoua.

“In a surprise attack Islamic State made an attack on positions held by the Free Syrian Army FSA groups which no one expected to happen so fast,” said Colonel Ismail Ayoub, a Syrian opposition army defector.

The militants launched a wide-scale dawn attack from their enclave where they are entrenched in the towns of Jamla, Ain Zakar Nafaa and al Shajra, deploying dozens of armored vehicles and several tanks to overrun nearby towns aided by sleeper cells among locals who helped the attackers, two rebel sources said.

The jihadists were later driven out of at least two villages - Jileen and Heet - after a counteroffensive by Southern Front groups, an alliance of FSA factions that coordinates operations from a joint command center in Jordan, said Abu Yahya, a rebel official in the Jabhat Thwar Surya faction.

It includes groups that have received some support from foreign states including Gulf Arab governments.

The Sunni hardline militants are members of the so-called Khalid Ibn Al Walid Army, a grouping set up last year from a merger of two main militant jihadist factions who are believed to have pledged allegiance to Islamic State and now control the strip of territory southeast of the Golan Heights.

Jordanian army units stationed along the border were put in a state of heightened readiness, a Jordanian security source said, and residents in the area said sounds of mortars were heard clearly from the fighting across the border.

A rebel official told Reuters that several FSA rebel groups were expected to get fresh supplies of arms from Jordan in the next few weeks to beef up their defenses against the ultra-hardline Sunni radicals.

Earlier this month the Jordanian air force said it conducted air strikes against the militants in the area, destroying an ammunition depot, a car bomb factory and barracks.

Militants had reportedly executed several people in Tseel, the largest town that fell into militants’ hands on Monday and which has been a haven for tens of thousands of displaced peoples

Tseel and most of the area captured by the militants had until early last year been in their hands until an alliance of FSA groups and rival Islamist groups wrested control and then managed to lay siege on their territorial enclave.

The ultra-hardline militants’ offensive came as heavy fighting between rebels and the Syrian army entered its second week in Deraa city, nearly 40 km (25 miles) east of the Yarmouk Valley, in the first such surge of violence in over a year and a half.

The timing of the Islamic State-affiliated group’s offensive has prompted accusations they had exploited the preoccupation of the FSA rebels in ongoing battles with the Syrian army.

Rebel advances in a strategic district held by the army have prompted Russia to wage an intensive bombing campaign of rebel-held parts of the southern city for the first time since Moscow’s major intervention in September 2015.

The capture of Manshiya district would put the remaining government-held part of the city within firing range of the rebels and thwart repeated army attempts to rupture supply lines linking rebel-held areas to the east and west of the city.</s>Rebel forces were caught completely off-guard overnight when hundreds of ISIS militants infiltrated the southwestern countryside of Daraa, capturing 5 sites (2 towns, 2 villages and 1 hill) in a huge blitz offensive in the region.

After initially targeting the towns of Tseil (Tasil) and Sahm Al-Joulan (Saham al-Jawlan), the ISIS-affiliated ‘Jaysh Khaled bin Waleed’ continued to attack and subsequently impose full control over the villages of Jellen (Jaylan), Adwan (Edwan), and the Al-Jomuaa hill on Monday morning.

The sites were reportedly poorly defended after Ha’yat Tahrir al-Sham (jihadist coalition) and Southern Front (Islamist coalition) redeployed hundreds of rebel fighters to Daraa city in recent weeks for its ‘death over humiliation’ offensive against the Syrian Arab Army (SAA).

If one is to believe Amaq Agency, 20 rebel fighters were killed during the advances.

Effectively, ISIS is now less than 10 kilometers from reaching government-held areas in Daraa province and some 15 kilometers from the provincial capital of Daraa.

Now, the two rebel coalitions must either call off their Daraa city offensive against the SAA or face the looming possibility of conceding more villages to ISIS in the hours to come.

ISIS controls a small enclave along the border with Israel and Jordan that is not directly connected to the Islamic State mainland. This area is composed of around 20 towns and villages under Jaysh Khaled bin Waleed command.

In March 2016, ISIS launched an offensive on the very same villages and towns but was kicked back by rebel forces the next month.

Jaysh Khaled bin Waleed was formed after the Yarmouk Martyrs Brigade and the Islamic Muthanna Movement merged last year. These groups defected from the Syrian Opposition in 2014.
The ISIL-affiliated Syrian opposition group Jaysh Khaled bin Waleed overwhelms Tahrir al-Sham and Southern Front militants, capturing the towns of Tasil and Saham al-Jawlan, along with two other villages and a hill in Daraa Governorate.