The Chechens, which Russian-backed Chechen president Ramzan Kadyrov allegedly dispatched to Ukraine's restive east, are a new face of Russia's interference in the country. Since the militants are not formal Russian soldiers, Russia can continue to deny its links to separatists in Ukraine.
"If they are Chechens, they are citizens of the Russian Federation. We can't control where our citizens go," a Russian foreign ministry official told the Financial Times. "But I can assure you that we have not sent our forces there."
Chechen fighters had reportedly taken part in the battle at the Donetsk airport, in which more than 50 pro-Russian separatists were killed during a heavy Ukrainian assault.
The presence of Chechens in Ukraine is worrying for a number of reasons. Chechen militants are known for being well-trained and formidable fighters. Chechnya was a war zone for most of the period between 1994 to 2009, and many Chechen militants received training from foreign jihadists who were assisting in the mostly-Muslim separatist movement's fight against Moscow.
Chechen fighters are also known for using incredibly brutal tactics. Terrorists from the region were responsible for a 2004 attack on a Russian school that left more than 300 dead.
The inclusion of Chechens also signals that the crisis in Ukraine could widen. Serbian ultra-nationalists already flocked to Crimea during the Russian invasion of the peninsula to help ensure order during the referendum that led to Russia's annexation of the region.
The Chechens, for their part, have sworn revenge against the Ukrainian government for the death of one of their militiamen in Donetsk.