NKVD special groups
The special groups of the NKVD for fighting against nationalists (Russian: Специальные группы НКВД по борьбе с националистами) were units set up by the People's Commissariat for Internal Affairs of the Soviet Union mainly in territories annexed by the USSR before the German-Soviet war due to the Molotov–Ribbentrop Pact, in particular they fought against the OUN and UPA in Ukraine (mostly Western), the Forest Brothers, in the Baltic states and against the Belarusian Black Cats, a special unit of the Schutzstaffel. They were also known as the Agent-Combat Groups (ABG), legend groups, false UPA detachments and the NKVD units dressed as UPA fighters.