Supporters of the Al Nusra Front take part in a protest against Syrian President Bashar al-Assad in Aleppo. The group is extending its control over a swath of territory in the northwest of the country that was until recently held by the moderate opposition. (FADI AL-HALABI/AFP/Getty Images)

The main al-Qaeda affiliate in Syria is extending its control over a swath of territory that was until recently held by the collapsing moderate opposition, jeopardizing U.S. plans to form a new rebel force to fight extremists.

Since routing two of the biggest Western-backed rebel movements last month from the province of Idlib, Jabhat al-Nusra has been steadily consolidating its position as the single most powerful military force in northwestern Syria.

The group has overrun towns and villages throughout the province, secured supply routes into neighboring Turkey and potentially paved the way for the establishment of an Islamic “emirate” — a competing entity to the “caliphate” declared last summer by the Islamic State in northeastern Syria and western Iraq.

The al-Qaeda affiliate’s expanding footprint risks further complicating the U.S.-led effort to contain and destroy the far more powerful Islamic State, a fierce rival to Jabhat al-Nusra that ejected the al-Qaeda loyalists from its territories last summer.

If the fighting in Syria continues on its current trajectory, the country soon will be partitioned almost entirely between jihadist forces and those of the Assad regime, leaving the moderate rebels without territory and the United States without allies in the strategically important country, rebel commanders and analysts say.

Members of Nusra Front drive in a convoy as they tour villages, which they said they have seized control of from Syrian rebel factions, in the southern countryside of Idlib. (Khalil Ashawi/Reuters)

Aid in the planning stages

Meanwhile, Pentagon plans to train and equip a force of 5,000 rebels in northern Syria to fight the Islamic State are still being formulated. A location south of the Turkish capital, Ankara, has been identified as a base for training the first 2,000 rebels, and the opposition has been given a date — Feb. 1 — for the first classes to begin, according to Syrian opposition representatives.

But U.S. officials have yet to meet with Syrian opposition leaders to discuss the program. They are still debating with Turkey which groups will be picked and have not yet finalized the questions to be asked in the vetting process.

Rear Adm. John Kirby, the Pentagon spokesman, said Thursday that officials are still waiting for funds to implement the program. The money was authorized later that day with the passage by Congress of a defense authorization bill.

By the time the process gets underway, there may not be any moderate rebels left to aid, said Yezid Sayigh of the Carnegie Middle East Center in Beirut.

The policy “assumes a continued viable presence of the moderate opposition inside Syria. The fact of the ascendence of Jabhat al-Nusra is rendering these ideas moot,” he said. “By the time these things become a reality on the ground, Nusra will have already acquired such a degree of control the policy will no longer be feasible.”

Rebel commanders say there is still life in the Free Syrian Army, the umbrella name used by moderate groups, even as it fights for its survival on two fronts, against the government and against the Islamic State. A covert CIA-run program to aid moderate rebels has helped hold off a government advance that threatens to dislodge them from Aleppo, their most important stronghold, located to the east of Idlib.

U.S. officials have said they are considering expanding that program in light of the recent setbacks, acknowledging the need for what one official called “a little more urgency.”

But while some rebel leaders say they have been promised increased resources, others say their support has been suspended since the Jabhat al-Nusra offensive. All say the limited aid in any case never amounted to enough to ensure their survival.

“If we see our support continue at the same levels we’ve had in the past, in the next three to six months we will see the moderate rebels disappear,” said Khalid Saleh, the spokesman for Harakat Hazm, the biggest recipient of U.S. support, which was ousted from its headquarters in Idlib last month by Jabhat al-Nusra.

Harakat Hazm is still fighting in Aleppo, alongside other moderate U.S.-backed groups such as Jaish al-Mujahideen, which was also recently vetted for assistance by the CIA and has received training and American-supplied weapons, including TOW antitank missiles, according to Abu Abdosalabman, one of the group’s leaders.

But the support is not enough, he said. “We’re on the borderline between staying alive and dying, and our immunity is low. If we are hit by a strong disease, we might not be able to survive.”

Jabhat al-Nusra’s hegemony

In the strategically vital province of Idlib, which borders Turkey, the moderates are all but vanquished, he and other commanders acknowledged.

Jabhat al-Nusra, which began as the Syrian offshoot of the Islamic State in Iraq before evolving into a separate Syrian entity after the Islamic State broke ranks with al-Qaeda, does not control all of the province’s territory. Numerous small moderate groups are still present, as are several larger Islamist formations that bridge the divide between moderates and extremists.

Most, however, have accepted Jabhat al-Nusra’s hegemony, at least for now, by staying neutral or forming alliances, said Abu Mohammed, a commander with the small Ansar al-Sham group, which has chosen neutrality in the fight between Jabhat al-Nusra and other rebel groups rather than risk annihilation.

“The situation in Idlib is very difficult now,” he said at his group’s office in the southern Turkish town of Antakya. “All of the remaining Free Syrian Army groups are afraid they will be kicked out.”

Although formally affiliated with al-Qaeda, Jabhat al-Nusra has earned a reputation among Syrians as the most effective force in the fight against Assad. It has also branded itself as a more disciplined and principled presence in local communities than the often unruly and sometimes outright criminal Free Syrian Army battalions.

The group has so far refrained from implementing the harshest forms of Islamic law associated with the Islamic State. Though Jabhat al-Nusra has declared its aim to create an Islamic “emirate” to rival the Islamic State’s “caliphate,” it has not yet done so, perhaps for fear of creating a backlash among Syrians whose main goal is to replace the Assad regime with a more democratic one.

The perception that U.S. airstrikes are helping Assad hold on to power has further served to increase sympathy for Jabhat al-Nusra at the expense of Western-backed groups, Syrians say.

Rebel commanders say it was all but inevitable that Jabhat al-Nusra would take on the moderates after President Obama announced the train-and-equip program in July, thereby creating an incentive to dispense with U.S.-backed groups before they received the infusion of support.

Their fate may have been sealed when U.S. airstrikes targeted Jabhat al-Nusra positions on the first day of the air war in Syria, signaling that the group was indeed on the American target list, said Aron Lund, who edits the Syria in Crisis blog for the Carnegie Endowment for International Peace.

“Nusra are not stupid. They know — first it’s Daesh and then we’re next,” he said, using an Arabic acronym for the Islamic State.