ISTANBUL -- The first Syrian rebel group to receive U.S. heavy weapons officially dissolved over the weekend after losing hundreds of men in back-to-back battles against Jabhat al-Nusra, the al Qaeda offshoot in Syria, officials from the group told International Business Times. The disintegration of Harakat Hazzm marks a turning point for the fight to control the surroundings of Aleppo, Syria's biggest city and economic center. The area, once controlled by what the U.S. considered moderate rebels who could be trusted and armed to fight President Bashar Assad, is now dominated by Sunni Muslim extremists.

Harakat Hazzm, the first Syrian rebel group to receive long-range TOW missiles from the U.S., fought in the northern countryside outside Aleppo. Some rebels defected, with their U.S.-supplied anti-tank missiles and personal weapons, to more extremist groups fighting in the area, while others folded into the Levant Front -- a combination of multiple rebel groups, some with connections to al-Nusra.

The breakdown of moderate forces in northern Syria and the rise of extremist groups is making it more difficult for the U.S. to pinpoint reliable allies in the region to support.

In the spring of 2013 the U.S. selected groups of rebels fighting within the Free Syrian Army, first through a classified CIA-led program, which was formally announced in August 2013. The program allowed for the transfer of U.S.-made weapons to Turkey via other countries’ aircraft. The weapons were then driven into Syria by truck. The program was partially funded by Saudi Arabia and other wealthy Sunni states.

But the emergence of the Islamic State, also known as ISIS or ISIL, set those rebels back. They had to fight on multiple fronts, against Assad and against ISIS, with little resources and dwindling U.S. support. 

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Harakat Hazzm, or "movement of steadfastness" in Arabic, began to lose ground in November when al-Nusra, also known as the Nusra Front, pushed it out of Idlib province. Al-Nusra took over the movement’s headquarters there and seized weapons, including some of the TOW missiles. In January, Hazzm lost control of one of the only two open border crossings between Turkey and Syria, the Bab al-Hawa crossing in northwestern Syria, on the road to Aleppo. Rebel groups linked to extremist factions took it over.

Last year, the U.S. ramped up efforts to support the moderate opposition and began training several thousand rebels at a secret base in Jordan. Since then, those rebels have failed to make any significant advances in Syria. In fact, they lost Homs, once dubbed the "heart of the revolution," to the Assad regime in May. But in November, IBTimes reported exclusively, the U.S. began pulling back its supplies of lethal aid to moderate groups in the north of the country.

Now, Syrian rebel activists in Washington say the U.S. is looking to arm rebels in the south that are gaining ground in battles against the Assad military. It is still unclear if the vetting process has begun for new rebel allies, but rebels in the north say pinpointing groups to support in the south is easier because the region lacks the presence of extremist groups like al-Nusra and ISIS.