The Russian government says it has sent troops to fight alongside Kurdish units in northwestern Syria and is providing weapons to Iraqi Kurds in a tactic that could upstage a long-standing U.S. alliance with the stateless ethnic group and increase Moscow’s influence in the region.

Russian and Kurdish officials say the Kremlin intends to keep a foothold in the area by cultivating ties with some Kurdish groups through weapons, ammunition and oil deals, building on its presence established through its relationship with Syrian leader Bashar al-Assad’s regime.

Russia’s support appears to be focused on one group in western Syria, the Afrin Kurds, an American defense official said.

The Afrin Kurds have not been backed by the U.S., which has supported an umbrella group of Syrian Kurdish fighters, known as the People’s Defense Units, or YPG.

The U.S. relies on Kurdish militants in Syria as one of its most effective allies in the fight against Islamic State. That support has angered Turkey, which sees the YPG as a threat for its close ties with the Kurdistan Workers’ Party, or PKK.