Two top U.S. diplomats are defending President Barack Obama’s policy to defeat Islamic State militants in Syria, and they say Russia’s intervention has destabilized the battlefield.

The two testified Wednesday before the House Foreign Affairs Committee – where both Democrats and Republicans are critical of the administration.

Assistant Secretary of State Victoria Nuland says that if Russia wanted to have a positive role, it would insist that Syrian President Bashar Assad ground the aircraft he’s using to bomb civilians. She says Russia also should work with the U.S. and its partners toward a cease-fire and political transition.

Assistant secretary of State Anne Patterson says that so far, U.S. diplomatic efforts have not led to any agreement about Assad.

(AP)