The researchers have been studying samples brought up from Vostok - the largest subglacial lake in Antarctica. Last year, the team drilled through almost 4km (2.34 miles) of ice to reach the lake and retrieve samples.
Vostok is thought to have been cut off from the surface for millions of years. This has raised the possibility that such isolated bodies of water might host microbial life forms new to science.
"After putting aside all possible elements of contamination, DNA was found that did not coincide with any of the well-known types in the global database," said Sergei Bulat, of the genetics laboratory at the St Petersburg Institute of Nuclear Physics.
"We are calling this life form unclassified and unidentified," he explained. Dr Bulat added that close attention was focused on one particular form of bacteria whose DNA was less than 86% similar to previously existing forms.