After Operation Barbarossa, the German military and Orpo aided by the Ukrainian Auxiliary Police battalions, began mass deportations of Polish inhabitants of Zamojszczyzna south of Chełm in preparation for the "Generalplan Ost" resettlement ordered by "Reichsführer-SS" Heinrich Himmler. Some Polish villages were simply razed and their inhabitants massacred. During "Heim ins Reich Ukraineraktion" , pro-Nazi Ukrainians and German-Ukrainian "Volksdeutsche" were being resettled there along with ethnic Germans from the east. They were given new latifundia built by Jewish prisoners of the Lublin Reservation who were sent to nearby Sobibór extermination camp afterwards. The Polish underground retaliated by launching the Zamość uprising, considered to be among the largest actions of the Polish resistance during World War II. Some Ukrainian sources refer to this operation as a massacre of Ukrainian villagers near Chelm and in the Podlasie area, and attribute thousands of those killed to the Polish underground. Such claims are rejected by the Institute of National Remembrance, and debunked by Ukrainian authors of the "Historical Dictionary of Ukraine" who point out that recent studies confirm a much lower figure. According to Jewish sources, the Jewish partisans themselves used to execute Ukrainian villagers "who had gone to the woods to round up the Jews who had escaped" from the ghettos. The killings in villages near the Parczew forest were motivated by revenge for the "anti-Jewish activities" of the Ukrainian peasants.