These are the elite Russian troops that are allegedly fighting some of the most crucial battles in Ukraine
But Russian soldiers are still believed to be operating along the front lines of the conflict.
US Army Europe commander Ben Hodges said while touring a NATO facility in Poland that it was obvious that there was direct Russian intervention around the strategically important Ukrainian city of Debaltseve.
Hodges' comments came shortly after Ukrainian military spokesman Andrily Lysensko warned that 1,500 Russian soldiers and 300 pieces of military equipment crossed into Ukraine from Russia on February 7 and 8.
Russian sources have corroborated some of the most serious allegations of Moscow's military involvement in the Ukraine conflict. Russian TV recently aired footage that seemed to clearly show Russian Naval Infantry, the country's equivalent to Marines, taking part in the fighting at Donetsk airport on January 20.
By January 22, after eight months of fighting, one of the Donbas's most critical pieces of infrastructure was in the hands of Russian-backed separatists.
Here's a map of the conflict so far.
Here's a look at some of the most elite soldiers that Russia has used to prosecute its war in Ukraine.
The Russian Naval Infantry was first formed in 1705 following a battle with Sweden during the Great Northern War. Its purpose was to carry out boarding and landing operations against enemy ships in the Baltic.
Since its inception, the Russian Marines have developed into one of the premier units within the Russian military.
Today, the Marines are spread throughout Russia. There is a division of Marines in the Pacific Fleet, independent brigades in the Northern and Baltic fleets as well as the Caspian Flotilla, and a regiment in the Black Sea Fleet.
Due to their small size - only around 12,000 men - the Russian Marines function as shock troops that carry out limited attacks and commando-style raids before the arrival of more conventional ground forces.
Russian Naval Infantry may have played a key role during the Russian annexation of Crimea.
After the takeover of the peninsula, a Russian Marine was accused of murdering an unarmed Ukrainian sailor.
Most recently, Russian Naval Infantry units have been spotted fighting alongside separatists in the crucial battle for the Donetsk airport in eastern Ukraine.
The Russian Naval Infantry has also been used in various conflicts. It's been used to fight the insurgency in Chechnya and in sea patrols against Somali pirates.
