AMMAN: Islamic State fighters in a convoy of roughly 100 cars captured the village of al-Mahsa in the eastern Qalamoun Mountains from a coalition of rebel groups Tuesday, reportedly cutting off a key desert supply line running from Jordan into the Damascus countryside, a local citizen journalist affiliated with participating rebel brigades told Syria Direct Wednesday.

“The battle resulted in nearly a hundred dead and missing among the rebel forces,” which included fighters from Jaish Usud a-Sharqia, Jaish al-Islam and other brigades, said the source, who goes by Abu Mujahid a-Shami.

A spokesman for one of the participating rebel brigades, who talked with Syria Direct Wednesday on the condition of anonymity, confirmed that IS had captured al-Mahsa.

 Jaish al-Islam fighter killed in al-Mahsa. Photo courtesy of Jaish al-Islam in Qalamoun.

IS's takeover of al-Mahsa means the “FSA's loss of the only supply line that begins in Jordan and ends in areas of Damascus and its countryside,” reported pro-Islamic State Amaq News Tuesday.

Abu Mujahid a-Shami confirmed that information: “it is indeed the only [rebel] supply route because the rest are under regime control.”

The rebel spokesman who preferred anonymity said that other routes were still operational, but that IS's capture of al-Mahsa “will make things more difficult” as far as moving supplies.

Rebel brigade Jaish Tahrir a-Sham reportedly facilitated IS's entry into the mountainous region, according to pro-opposition Rasd Souria. Jaish Tahrir a-Sham had previously denied rumors that its leader, Firas al-Baitar, had pledged allegiance to the Islamic State.

The rebel spokesman confirmed that Jaish Tahrir a-Sham had facilitated IS's attack on al-Mahsa.

IS's takeover of al-Mahsa comes on the heels of a series of victories in Syria's eastern desert region, including Aada Mountain in eastern Homs last week, and Tel Dakwa in eastern Qalamoun in February.