ISTANBUL—Russia has sent new forces to a regime-controlled airfield in northeastern Syria as American military advisers step up operations with Kurdish militants in the same region, according to U.S. and Turkish officials.

The parallel military moves, while small, could create new friction between Washington and Moscow, where leaders are angling to protect their competing interests in Syria and shape the direction of peace talks aimed at ending the five-year conflict there.

The new deployments to northeastern Syria come as world leaders are struggling to launch United Nations-brokered talks next week in Geneva, with unresolved disputes between rival factions threatening to derail the negotiations before they begin.

With few expecting much progress from the talks, Russia and the U.S. are maneuvering for more influence in key Syrian battlefields.

The U.S. military is stepping up its operations in northeastern Syria as teams of special-operations forces deepen their engagement with Kurdish and Arab militants leading the fight against Islamic State.