On Sept. 12, Islamic rebels in Syria declared war … on their fellow rebels. Two Al Qaeda-linked extremist rebel groups—Al Nusrah and the Islamic State of Iraq and Al Sham, a.k.a. ISIS—followed up their declaration with an attack on the main Free Syrian Army.

The two-year-old Syrian civil war is now officially a three-way fight, pitting the regime of Pres. Bashar Al Assad versus the FSA versus the Islamists.

In other words, an unholy mess.

On Sept. 18 extremist forces attacked the moderate rebels in Azaz, on the outskirts of Aleppo in northern Syria. Details on the fighting have been provided by the Syrian Support Group, a U.S.-based organization that is certified by the State Department to provide non-lethal aid to the FSA.

“The firefight began when ISIS tried to kidnap a German doctor working in an Azaz hospital with Doctors Without Borders,” the Syrian Support Group reported. “Fighters protecting the doctor refused to allow him to be taken. ISIS then began shooting, and the fighting spread throughout the town in short measure.”

At least six people died in the attack including activists, doctors and FSA fighters, according to the support group. Another 15 people were reported captured by the Islamists, adding to the many hundreds of prisoners already being held—and in some cases tortured—by extremist rebels.

The Islamist assault forced Turkish authorities to shut down a nearby border crossing that is a major transit point for humanitarian aid. “There is still confusion about what is happening on the Syrian side. All humanitarian assistance that normally goes through the gate has ceased,” a Turkish official told Reuters.

FSA reinforcements are rushing to reinforce the border, the Syrian Support Group claimed. “Unfortunately, Azaz itself is now fully under ISIS control.”

The U.S. provides weapons, supplies and some training to the FSA, and is keeping warships and jet fighters near Syria to keep pressure on Al Assad to give up his chemical weapons as promised.

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