Last weekend, Al-Qaeda-affiliated fighters in northern Syria executed a prominent moderate rebel commander—a slaying that has exacerbated divisions between Islamic militants and degraded morale inside the beleaguered Western-backed Free Syrian Army (FSA), which is facing a defection crisis.

The slaying of Ammar al-Wawi by jihadists linked to the Islamic State of Iraq and al-Shams, or ISIS, is the latest in a series of targeted abductions and assassinations of leading moderate rebels. FSA sources say they suspect that al-Wawi was executed on Saturday after being cornered three days earlier, along with three of his men, near Bab al-Hawa as he crossed back into Syria from Turkey.

A few days before his abduction, fighters with the newly-formed Islamic Front seized FSA weapons storehouses at Bab al-Hawa. The Front has no official ties with the al-Qaeda fighters—who see the Syrian civil war as part of their global jihad—but it shares much of their hardline ideology and several of the seven brigades that make up the Islamic Front have fought alongside jihadists in the past.

Al-Wawi, a former Syrian government intelligence officer who defected to the rebel cause in July 2011, was a regular interlocutor with the international media, often serving as the FSA’s spin-doctor in videos uploaded to YouTube and in interviews with Arabic-language television channels.

More than a year ago, al-Wawi was apparently upbeat about the prospects of the rebellion against President Bashar al-Assad, saying that the regime was “like the walking dead.” Now, his execution has added to a sense of foreboding among brigades still aligned with the FSA.

In July, jihadists killed popular FSA commander Kamal Hamami, a member of the rebel supreme military command, after luring him to a meeting in the Jebel al-Krud region, north of Latakia. His body was mutilated before being dumped. In early December, two other FSA commanders were assassinated in northern Syria.

The assassinations, along with the suspension earlier this month of non-lethal aid to the FSA by the U.S. and Britain following the seizing of the Bab al-Hawa weapons storehouses, has compounded a sense of doom in the ranks of the Western-backed rebel coalition. The al-Qaeda affiliates ISIS and Jabhat al-Nusra and the Islamic Front are gaining in strength as a result and attracting defectors from the FSA.

Last week, the FSA renamed itself the Syrian Rebel Front (SRF), representing 14 different factions. With Turkish government go-betweens, it has been seeking to find some common ground with the hardline Islamist groups. But few believe that renaming the FSA will change the fortunes of the more moderate rebels—ones not wedded to the idea that a Sharia law-based Islamic government should replace Assad’s regime.

In a report for the Carnegie Endowment, Aron Lund, who has long followed the Syrian rebel groups, says that while foreign funding could help the group become a significant force, unity could prove elusive as “there’s little to indicate that the SRF’s creation is underpinned by any real ideological or political agenda. Instead, it seems very much to be a case of coming together against a common enemy—the Islamist surge in general and the Islamic Front in particular.”

The overall commander of the Syrian Rebel Front, Gen. Salim Idris acknowledged in an interview last week with PBS that “the situation in the north of Syria now is very complicated and very dangerous, because there are some problems between some groups, and I think we should try everything now to find a solution for this problem.”

That includes talking with Islamic Front—an approach the Obama administration is now adopting as U.S. officials prepare to talk this week in Turkey with Islamic Front leaders, according to State Department sources. The Islamic Front representatives have apparently asked for arms supplies. “We need to try to adapt to changing circumstances and try to keep the Islamists apart from the jihadists,” a State Department official told The Daily Beast’s Josh Rogin earlier this month.

The tactic not only is prompting alarm among some U.S. lawmakers but among opposition activists who say relations between the Islamic Front and the jihadists are closer than the Islamic Front readily acknowledges, and that the al-Qaeda affiliates are now inseparable from the rebellion. One of the key figures in the Syrian Rebel Front, Jamal Maarouf, who commands the Syria Martyrs Brigade, has agreed to al-Nusra acting as a go-between in a dispute between his militia and the Islamic Front.

The planned Geneva II peace talks are adding urgency to the Obama rethink as the administration searches for a way to engineer a rebel consensus. But the Islamists have already rejected peace talks and have little reason to negotiate: their ranks number three times as large as the FSA’s—analysts estimate they command about 45,000 fighters—and they seem to have the support of Saudi Arabia.

On the battlefield, as rebel divisions plague the uprising, overall momentum continues to shift to Assad as Syrian army forces, aided by fighters from Hezbollah, push forward on offensives on three fronts—on the eastern approaches of Aleppo, the southern suburbs of Damascus and in the mountainous region of Qalamoun, adjacent to the border with Lebanon.

The Syrian Observatory for Human Rights, a UK-based monitoring group that relies on information supplied by a network of opposition activists, says government forces has escalated their assault on rebel-held neighborhoods in Aleppo with air strikes on 13 districts that reportedly left up to 118 civilians dead, including more than two dozen children. In the air strikes so-called barrel bombs—explosive-filled oil barrels—were used, prompting protests from UNICEF, the United Nations Children’s Fund. Maria Calivis, the agency’s regional director for the Middle East, said the indiscriminate slaughter was unacceptable.