ROBERT SIEGEL, HOST:
The brutal extremists who call themselves the Islamic State continue to hold large parts of Iraq. And now, the power they hold there is giving them an upper hand in their fight in Syria. As NPR's Alice Fordham reports, the group successes are attracting more supporters.
(SOUNDBITE OF YOUTUBE VIDEO)
UNIDENTIFIED MAN: (Foreign language spoken).
ALICE FORDHAM, BYLINE: The bearded Syrian rebels gather in a circle and look resentful, as they swear an oath of allegiance to the Islamic State. This video, posted on YouTube, shows one of a cascade of Syrian pledges of support to the group so extreme that even al-Qaeda rejects them.
Once, less extreme rebels fighting President Bashar al-Assad also battled these hardliners, but that's changed. An analyst for the D.C.-based Institute for the Study of War, Jennifer Cafarella, says that the Islamic state scored a propaganda victory when they took much of Western Iraq.
JENNIFER CAFARELLA: I definitely think that the psychological aspect of this is significant and I think that a lot of this can be attributed to the dilemma that is caused within the Jihadi to community by the declaration of the caliphate.
FORDHAM: It's not because of a religious obligation. In fact, Syrian rebels initially rejected that caliphate, an Islamic Empire declared by the Islamic State. Nor is it because the extremists have yet used all the money and weapons they acquired in Iraq.
CAFARELLA: We haven't actually seen a full-scale ISIS advance in Syria.
FORDHAM: Rather, it's the effect of seeing the Islamic State conquer so much turf that it made them seem an irresistible force in Syria too. Now, the extremists control nearly all the towns along the Euphrates River that flows from Syria into Iraq. And moderate Western-backed rebels gave up fighting even before the recent events. Lieutenant Colonel Mohamed Abboud, a commander of the eastern front, says he quit because his Western sponsors never sent him money or weapons, even when he fought against the extremists.
LIEUTENANT COLONEL MOHAMED ABBOUD: (Foreign language spoken).
FORDHAM: He says, we'd get called on by the revolutionaries and the civilians inside, and they'd ask, why aren't you doing anything for us? Why aren't you providing us any support? There's been another crucial change. The Islamic State rarely took on Assad's forces directly, preferring to consolidate control of rebel-held areas. But this month, their fighters have confronted regime soldiers over a gas field and surrounded an army base close to the city of Raqqa. The group has claimed, their flag flutters across all the land, between central Syria and Eastern Iraq. It wasn't quite true, but they're only getting stronger.
Alice Fordham. NPR News, Beirut. Transcript provided by NPR, Copyright NPR.