The special groups of the NKVD for fighting against nationalists (Russian: Специальные группы НКВД по борьбе с националистами)[1] 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.
In 1944 the Red Army moving to the west reconquered the territory of Western Ukraine that was occupied by Nazi Germany and its allies in 1941.
In March 1944, in response to the situation, the NKVD Operational Headquarters was set up in Rivne to combat the Ukrainian national liberation movement.
Since the second half of 1945, on the instructions of the UPA command, large units of the Ukrainian Insurgent Army began to be reorganized into well-united and armed smaller ones, that were deployed in forests.
In addition, the extensive secret underground networks were created in rural areas, each had 10-15 people, and was called "boyivka (боївка)" - a militant group.