WASHINGTON (Reuters] – A senior U.S. defense officer stated that Russia may have used a short range missile to attack a Ukrainian train station.

Ukraine claimed that at least 50 civilians were injured and killed by a Russian strike in Kramatorsk. The attack was on a station located in the city.

An American defense official spoke under anonymity and said that although the Pentagon thinks Russian forces used an SS-21 Scarab ballistic missile, it was unclear why.

NATO uses the SS-21 acronym to describe a type missile, the Tochka.

Officials from the United States said that the United States is still reviewing the strike. It was not clear if any cluster munitions were employed.

The official stated that “We don’t buy the Russians’ denials that they were not responsible.”

RIA News Agency quoted Russia’s defense ministry as saying that missiles believed to have been fired at the station were not used by Ukraine’s military, and that Russia had no designated targets in Kramatorsk by Friday.

Recent social media videos, which Reuters couldn’t independently verify, show Russian troops in Ukraine or nearby transporting Tochka missile-launchers.

According to the U.S. defense officials, Russia’s military power in Ukraine was still declining and it was between 80%-85% of pre-invasion levels.

Before the invasion by Russia on February 24, 2018, it was estimated that Russia had assembled over 150,000 troops in Ukraine.

According to the official, there are now indications that Moscow is mobilizing some reserves and may be seeking out more than 60.000 personnel.