Syrian rebels who are known as Free Syrian Army are battled extremist suspected of links to the ISIS group in a southern province near the Golan Heights, with at least 29 people killed in days of clashes, a spokesman and activists said Wednesday.

The ISIS group is not known to have a significant presence in southern Syria.

However, Isam al-Rayess, spokesman for the Free Syrian Army’s Southern Front, said a group known as Jihad Units, also known as Jaish al-Jihad, ambushed some of his fighters in the Quneitra province who were on their way to join an offensive against Syria Army.

He said the Southern Front, a rebel coalition, has long suspected of being loyal to the ISIS group.

After the ambush, the fighters raised black flags similar to those carried by the ISIS group.

Six of the Southern Front fighters were killed in the ambush, al-Rayess said. Soon after, another ambush resulted in the kidnapping of two fighters, he said.

The Britain-based Syrian Observatory for Human Rights said 29 people, including at least nine from the Jihad Units and two Saudi nationals, have been killed in the fighting since Monday.

On Tuesday, two mortars from the fighting landed on the Israeli occupied side of the Golan Heights, in what was seen as errant fire.

The rebels have vowed to clear the Jihad Units from the province, and al-Rayess said his men are currently besieging about 200 Jihad Units fighters in a village south of Quneitra.

Fighters from the al Qaida-affiliated Nusra Front and Ahrar al-Sham, a hardline Islamic rebel group, have also joined in the fight against the Jihad Units, al-Rayess said, although there is no coordination.

“We will not allow for the presence of Daesh in the southern front,” al-Rayess said in a telephone interview.