A Russian paramilitary group asked for intel on Latvia, Lithuania and Estonia, The Guardian reported.
The call raised concerns about "rogue actions" in NATO states, a source told the paper.
Task Force Rusich, which has close ties to the Wagner Group paramilitary group and has been highly active in Ukraine, posted the appeal on its official Telegram channel on December 7, the paper reported.
All three countries mentioned by Rusich's post are NATO member states, raising concerns over moves that could escalate the war.
The group, known for its brutality, openly advocated torture of prisoners in September, The Guardian reported at the time.