ISTANBUL — American proxies are now at war with each other in Syria.

Officials with Syrian rebel battalions that receive covert backing from one arm of the U.S. government told BuzzFeed News that they recently began fighting rival rebels supported by another arm of the U.S. government.

The infighting between American proxies is the latest setback for the Obama administration’s Syria policy and lays bare its contradictions as violence in the country gets worse.

The confusion is playing out on the battlefield — with the U.S. effectively engaged in a proxy war with itself. “It’s very strange, and I cannot understand it,” said Ahmed Othman, the commander of the U.S.-backed rebel battalion Furqa al-Sultan Murad, who said he had come under attack from U.S.-backed Kurdish militants in Aleppo this week.

Furqa al-Sultan Murad receives weapons from the U.S. and its allies as part of a covert program, overseen by the CIA, that aids rebel groups struggling to overthrow the government of Syrian president Bashar al-Assad, according to rebel officials and analysts tracking the conflict.

The Kurdish militants, on the other hand, receive weapons and support from the Pentagon as part of U.S. efforts to fight ISIS. Known as the People’s Protection Units, or YPG, they are the centerpiece of the Obama administration’s strategy against the extremists in Syria and coordinate regularly with U.S. airstrikes.

Yet as Assad and his Russian allies have routed rebels around Aleppo in recent weeks — rolling back Islamist factions and moderate U.S. allies alike, as aid groups warn of a humanitarian catastrophe — the YPG has seized the opportunity to take ground from these groups, too.

In the face of public objections from U.S. officials and reportedly backed by Russian airstrikes, the YPG has overrun key villages in the northern provinces of Aleppo and Idlib. It now threatens the town of Azaz, on the border with Turkey, through which rebel groups have long received crucial supplies. Over the weekend, Turkey began shelling YPG positions around Azaz in response, raising another difficult scenario for the U.S. in which its proxy is under assault from its NATO ally.

Yet as America has looked on while Russia and Syria target its moderate rebel partners, it has failed to stop the YPG from attacking them too. “That is a major problem,” said Andrew Tabler, a Syria specialist at the Washington Institute for Near East Policy. “It’s not just that it’s a nonsense policy. It’s that we’re losing influence so rapidly to the Russians that people just aren’t listening to us anymore.”

Othman, the Furqa al-Sultan Murad commander, said the YPG tried to seize two areas of Aleppo under his control, resulting in firefights that left casualties on both sides. He had captured seven YPG fighters and was holding them prisoner, he added.

Othman’s group receives weapons from the U.S. and its allies, including TOW anti-tank missiles, he said, and fights Assad as well as ISIS. The aid is part of a long-running CIA effort approved by Congress and coordinated from an operations room in Turkey with participation from international allies of the rebellion such as Saudi Arabia. Othman said he was in regular contact with his American handlers about the problems on the ground. “The Americans must stop [the YPG] — they must tell them you are attacking groups that we support just like we support you,” he said. “But they are just watching. I don’t understand U.S. politics.”