President Barack Obama's national security adviser says the U.S. now talks "almost daily" with Russia to ensure its military operations in Syria don't clash.

Susan Rice is speaking at the U.S. Air Force Academy. She says the U.S. and Russian governments are working together to investigate ceasefire violations and "build common ground" among Syrians.

Such frequent military-to-military discussions reflect a change. The U.S. suspended military ties after Russia annexed Crimea in 2015. But simultaneous U.S. and Russian air campaigns in Syria fueled concerns about a dangerous aerial incident.

Rice's remarks come amid other major military strains between the two countries. The U.S. said Thursday it had raised concerns with Russia through a U.S. military representative in Moscow after Russian military jets buzzed a U.S. Navy ship in the Baltic Sea.