(Washington, DC) -- The U.S. is increasingly concerned about the flow of weapons from Russia to rebels in eastern Ukraine. White House spokesman Josh Earnest told reporters today that the weaponry has fueled the ongoing violence there. He also cited "tragic consequences" after the crash of a Malaysian airliner in eastern Ukraine last week. Nearly 300 people were killed in the crash, which has been blamed on a ground-to-air missile. Earnest warned of additional sanctions against Russia unless Moscow changes course.