An Islamic State-affiliated group on Monday captured territory in south-western Syria, near the convergence of the Israeli and Jordanian borders, after launching a surprise attack on more moderate rebel fighters near the Golan Heights.

The Khalid Ibn Al Walid Army used dozens of armored personnel carriers and several tanks in a dawn attack against positions held by the Free Syrian Army, rebel sources said, according to Reuters.

“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,” Colonel Ismail Ayoub, a Syrian opposition army defector, said.

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Jordanian army units on the border were ordered to assume a heightened state of readiness, a Jordanian security source said; explosions from the battle could be heard across the border.

The fighters gained control of several villages and a large town — Tasil, Sahem el-Golan, Adwan, and Tel Jamoua — that lie about 11 kilometers (6.8 miles) from the Israeli border on the Golan Heights. The area is close to where the Israeli, Jordanian, and Syrian borders converge, near the Yarmouk River. They later lost some of the territory in a counterattack by the Southern Front groups, an ally of the FSA that runs its operations from a command center in Jordan.

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In Tasil, the largest town captured, where there are tens of thousands of people displaced by the war, the gunmen were said to have executed several people.

FSA rebels are reportedly expecting to receive supplies of arms from Jordan in the coming weeks as they continue to fight against IS and to try to bring down the Syrian regime.

Reuters reported that earlier in February the Jordanian air force said it bombed militant targets, destroying a car bomb factory, barracks, and an ammunition depot.

In November 2016, a short exchange of gunfire between the Khalid Ibn Al Walid Army and Israeli troops ended with an IDF airstrike that killed four militants. No IDF soldiers were injured in the incident.

A nearly six-year-long civil war in Syria that began as an attempt to overthrow President Bashar Assad has, in the southwestern area of the country, descended into a contest for territory between several rival militias, IS, and the Syrian army. Russia and Iran have given military support to Assad, while a US-led coalition is backing moderate rebel groups in their battles to defeat more extreme fighters.

Times of Israel staff contributed to this report.