“During the siege, we were hit with 50 ISIS car bombs,” Mu’tasim Abbas told me. “Each car was filled with 10 tons of explosive.”

Abbas is the commander of the Mu’tasim Brigade (the name, he assures me, is just a coincidence), one of a mere handful of Syrian rebel groups backed by the U.S. Department of Defense to defeat ISIS.

“I’ve been fighting them for three and a half years,” Abbas said, in an often digitally shaky Skype conversation. “I joined the Pentagon’s ‘train and equip’ program a year and a half ago and started coordinating with the U.S. to get my men trained in Turkey and to call in U.S. airstrikes.”

Based in the city of Marea in Aleppo province, the Mu’tasim were recently able to break ISIS’s weeks-long siege, which had in effect cut the rebels off from their comrades in Azaz, at the Syrian-Turkish border.

Before they broke the siege, Abbas’s men—around 400 in total—were unable to receive ground resupply from the United States even as they faced an onslaught of 1,000 well-armed and well-trained jihadists, about the same number that reportedly held Fallujah in Iraq until it was retaken by Iraqi forces at the weekend.

“ISIS are highly skilled, very ready and mentally prepared,” Abbas said. “After they get cornered, they’ll blow themselves up and not get taken alive.”

The Mu’tasim Brigade’s fortunes began to turn two weeks ago when it became the first ever exclusively Sunni Arab rebel militia in Syria to receive airdropped U.S. supplies.

Abbas gave me an inventory of U.S. Central Command’s largesse. The first airdrop (and there have been several since) consisted of “70,000 bullets for Kalashnikovs, 40,000 bullets for PKS [machine guns], 100,000 mortars [mortar shells].”

The trouble is, every time ISIS attacks the Mu’tasim Brigade, it cost the latter more than double those amounts for every type of ammunition. Ammo for heavier firepower, such as recoilless rifles, has occasionally made its way to Marea but, curiously, not in the latest exigent supply runs.

Commander Kyle Raines, a CENTCOM spokesman, told The Daily Beast: "When we conduct resupply missions, they are given standard equipment ranging anywhere from weapons and ammunition to communication gear."

Within days of receiving the airdropped cargo, the rebels managed to expel ISIS from four villages between Marea and Azaz, and four more along the Turkish border.

“The number of ISIS fighters was minimal because they had retreated,” Abbas said. He credits heavy U.S. airstrikes with “scattering” the enemy and reckons that around 350 jihadists were killed in the breaking of the Marea siege.

However, even more important than the recapture of vital terrain is the morale boost U.S. provision has given to rebels inside Aleppo. Abbas claims that the Mu’tasim Brigade has fielded hundreds of applications from other militiamen in Marea to join up with it.

“We are now 400, approved by the Pentagon, with 50 who have been trained directly by the U.S. military. But after the last week we could easily reach 1,500. These new recruits have to be approved first.”

Assuming any or all of them were to go for basic training in Turkey, how long would that take? “Anywhere from 15 to 45 days,” Abbas answered. “And sometimes as few as nine days.” But, he insists, everyone seeking to join the Mu’tasim Brigade already knows how to fight. They just need the hardware to carry on.

I asked him what the Pentagon’s protocol for approving new fighters consists of, particularly in light of the serial embarrassments (kidnappings by al Qaeda, auctioned-off gear to al Qaeda) of previous train and equip graduates.

“We ourselves vet the names before we submit them to the Americans,” Abbas explained. “Then the Pentagon checks these names against Interpol or national counterterrorism lists.”

So basically the already-approved rebels themselves are asked to vouch for the integrity and non-extremism of new enlistees and, provided no one turns up on an international no-fly or wanted list, the newbies are in the program? “Yes.”

Thus far, it has worked to the Mu’tasim Brigade’s advantage that its commander sees ISIS and the official al Qaeda franchise Jabhat al Nusra as graver threats to Syria than even the Assad regime, which has killed and displaced far more people nationwide. This is by no means a view commonly held by others Arab insurgents who originally took up arms against Damascus.

“When extremist groups started festering in our society, we specialized in fighting them. We redirected our battles just to fighting ISIS and other extremists who we believe are jeopardizing Islam and our existence.

“Once we get rid of ISIS,”Abbas said, inverting the usual rebel priorities, “then the regime will crumble.”

As for the Mu’tasim Brigade’s relationship with America’s principal ground proxy, the Kurdish-led Syrian Democratic Forces (SDF), here he does sound like most Arab insurgents. Marea wasn’t just besieged by ISIS on its eastern flank; it was also besieged by the SDF on its western flank.

“We feel a lot of animosity toward them. We tried to get a lot of our injured out through ambulances but we were rejected multiple times. Recently, the SDF did allow the injured out, but it’s a one-sided treatment. They started the siege against Marea.”

Abbas believes in U.S. reassurances that an independent or semi-autonomous statelet of Rojava—what Kurds call Syrian Kurdistan—is not one of the intended side effects of a Kurdish-led campaign against ISIS in the north, now focused on the so-called Manbij pocket, east of Marea, where ISIS is now completely surrounded.

The coalition’s plan is to allow Arabs in these liberated areas to govern themselves once the ISIS fighters are driven away by a Kurdish vanguard, a hopeful—not to say utopian—deference to pluralism in a part of the world not well known for it, especially of late.

The success or failure of that policy could mean the success or failure of keeping ISIS permanently out of areas it once ruled in Syria.

In their recent “dissent cable” lambasting the Obama administration’s Syria policy, 51 State Department officials expressed their pessimism about the prospects for this strategy. The Kurds, they wrote, “cannot—and should not—be expected to project power and hold terrain deep into non-Kurdish areas.”

For Abbas, it’s even simpler. Demography, he believes, is destiny. “There are thousands and thousands of Arab families in that area,” he said, “and there’s no way the Kurds can create [Rojava] without obliterating both sides.”

Internecine fighting between Arabs and Kurds has already been well-documented across northern Syria. Amnesty International has accused the YPG militias, the main fighting arm of the SDF, of razing Arab homes and forced displacement of local residents, actions that amount to war crimes.

Some Arab rebel groups, such as the Saudi-backed Army of Islam, have also shelled or rocketed the YPG in Aleppo, killing civilians and, in one instance, allegedly using chemical agents—a claim the Army of Islam’s spokesman refutes.

Last week, the London-based Syrian Observatory for Human Rights reported that the Mu’tasim Brigade destroyed a YPG bulldozer outside Marea with a TOW anti-tank missiles, a staple of CIA-backed rebel groups in Syria. Several of these munitions were indeed spotted in the area, but Abbas swears his men didn’t fire any: “The U.S. never gave us any TOWs. If we’d had or shot one, we would have issued a press release.”

In fact, Abbas badly wants and needs anti-tank missiles, as well as night-vision goggles and armored vehicles, all of which ISIS has in ample supply. He can’t understand why the United States has provided them given the Mu’tasim Brigade’s proven effectiveness and reliability—not to mention fortitude.

In late May, the brigade was hit by U.S. warplanes in a friendly fire incident Washington has since acknowledged. And before that, it was also targeted by the Russians in what was by no means the first time Moscow has struck U.S. assets in Syria.

Just last week, Russian Su-34s conducted a “double tap” bombing run against U.S. and U.K.-trained anti-ISIS rebels at al-Tanf, near the Jordanian border in eastern Syria, forcing the U.S. Navy to scramble two F/A-18 fighter jets, which flew close enough to visually identify the Russian bombers.

When the F/A-18s left to refuel, the Su-34s returned and bombed the rebels a second time. It was the boldest provocation yet by the Russians; though all it prompted was a U.S. commitment to better “coordinate” with them.

“Four months ago, we were attacked very strongly by the Russians and the regime because the regime tried to open the road to Nabul and Al Zahra,” Abbas said, referring to two rebel-besieged Shia villages in Aleppo. The Kurds, meanwhile, were busy retaking the border town of Tal Rifaat from ISIS.

“So Mu’tasim was attacked. We were surprised. Why would we be hit by the Russians when we were only fighting ISIS?”

What assurances have the Mu’tasim Brigade been given by CENTCOM that they’ll be protected from further Russian or regime sorties? “None,” he answered.

This piece has been updated since publication to include a comment from CENTCOM.