Augustów roundup The Augustów roundup ( Polish " Obława augustowska " ) was a military operation against the Polish World War II anti - communist partisans and sympathizers following the Soviet takeover of Poland . The operation was undertaken by Soviet forces with the assistance of Polish communist units , and conducted from July 10 to July 25 , 1945 in Suwałki and Augustów region ( Podlasie ) of northern People ' s Republic of Poland . Out of 2 , 000 arrested by the Soviet forces , about 600 have disappeared . They are presumed to have been executed and buried in an unknown location in present - day Russia . Polish Institute of National Remembrance has declared the 1945 Augustów roundup " the largest crime committed by the Soviets on Polish lands after World War II " . The crime has been called " second Katyn " , " small Katyn " , " little Katyn " or " Podlaski Katyn " , in reference to the Katyn massacre , the Soviet execution of about 20 , 000 Polish soldiers and intellectuals that occurred in the early 1940s . Background . In the aftermath of the joint German - Soviet invasion of Poland , the Polish government evacuated to the West and created the Polish Underground State . While no war was declared between Poland and the Soviet Union , the relations were tense , and eventually broke down in 1943 in the aftermath of the revelations of the Katyn massacre . The Soviets eventually created their own Polish communist puppet government , the Polish Committee of National Liberation ( " Polski Komitet Wyzwolenia Narodowego " , " PKWN " ) and refused to deal with the Underground State just like they refused to deal with the government - in - exile ; its leaders and soldiers on " liberated " Polish territories were persecuted . While the Underground State ' s military arm , " Armia Krajowa " , officially disbanded on January 19 , 1945 to avoid armed conflict with the Soviets and a civil war , some refused to lay down their arms ; others found it simply difficult to return to civilian life , as those with ties to non - communist resistance were discriminated against by the authorities . Operation . The operation was undertaken by Soviet forces of the Red Army , the NKVD and SMERSH with the assistance of Polish UB and LWP units , and conducted from July 12 to July 28 , 1945 in the Suwałki and Augustów regions of northern People ' s Republic of Poland . This operation included not only Polish communist territories , but also former Polish territories annexed by the Soviet Union and given to the Lithuanian SSR ( see Soviet occupation of Lithuania ) . Aftermath . More than 2 , 000 Polish ( some estimate as many as 7 , 000 ) alleged anticommunist fighters and sympathizers were arrested and interrogated in two waves of mass arrests . The majority were detained in Russian internment camps . The last ones were released and returned to Poland in 1956 . 600 have disappeared , their fate uncertain to this day . More recent research puts the number of those disappeared at 592 or 593 . They include 27 women ( including pregnant ones ) and 15 children under the age of 18 . The " Augustów Missing " are presumed to have been executed and buried in an unknown location in present - day Russia . Despite demands from many Polish citizens for this incident to be investigated , it was denied by both the Soviet and Polish communist governments . As late as the 1980s , the last decade of the People ' s Republic of Poland , government representative Jerzy Urban declared that the Polish government had " no evidence to support the theory that a group of Polish citizens disappeared in the Augustów region in 1945 . " After the fall of communism , the new Polish government supported the investigation , carried out by the Institute of National Remembrance ( IPN ) , which classified it as a communist crime . While it is commonly accepted that the Soviet Union , backed by communist Polish forces , arrested and likely executed approximately 600 Polish citizens connected to the anti - communist resistance , no conclusive information on their exact fate and resting place has yet been found . In 1995 the Russian government confirmed that 590 Polish citizens were arrested and 579 were put on trial , but that there is no information on their subsequent fate . In 2005 IPN noted that the research possibilities on Polish territory had been exhausted ; even the archives of Polish secret services involved in the operations were analysed but contained only cursory information that they were aiding the Soviets without being given much information . However , Polish requests to the Russian government for support in the investigation were not productive , and many have been ignored . A symbolic monument has been built in the village of Giby , where a mass grave was found ( these were later proven to belong to German soldiers from a nearby field hospital ) . In May 2011 , Russian historian Nikita Pietrov declared that he found a KGB document proving that the Poles were executed by NKVD . This has evoked interest in Polish mainstream press and from the IPN , which declared that it would seek the documents located by Pietrov for further analysis . On 18 April 2012 Polish Institute of National Remembrance announced that it has received the Soviet - era documents concerning the executions .