The Russian Defence Ministry on Monday cast doubt on pictures that Washington said showed Russia had recently shelled Ukrainian military positions.
The United States has accused Russia of instigating the conflict in eastern Ukraine where pro-Moscow separatists are fighting central government forces. Russia has denied any involvement in the conflict.
On Sunday, the US State Department released images it said showed Russian forces had fired across the border at the Ukrainian military.
Defence Ministry spokesman Igor Konashenkov questioned the substance of the images in remarks to journalists, according to RIA Novosti news agency. "Such materials weren't posted on Twitter coincidentally, since it's impossible to establish their authenticity due to the lack of exact reference to the location and the extremely low resolution," Konashenkov said.
The images showed marks on the ground at what US officials said were launch sites and impact craters around Ukrainian military locations, and indicated fire from multiple rocket launchers, the State Department said.