The State Department has released images of soldiers in eastern Ukraine that it says are Russian forces, showing militants wearing similar uniforms and brandishing Russian weapons.
The pictures mark the latest effort by the West to prove that Moscow is using its military to stir unrest in Ukraine.
A copy of the 11-page State Department document was given to reporters.
It includes pictures captioned as "concerned citizens" in Crimea and the city of Slovyansk who are dressed the same and carrying the same kind of RPG-30 rocket launchers that are issued to Russian troops.
There was no way to immediately verify the photographs, which were either taken from the Internet or were given to the Organization for Security and Cooperation in Europe last week by Ukraine diplomats.