the villages of Slankamen on the Danube and Boljevci on the Sava. However, after pressure from the NDH supported by the German ambassador to Zagreb, Siegfried Kasche it was gradually fully transferred to NDH control with the approval of the Military Commander in Serbia, and became a formal part of the NDH on 10 October 1941. The local Volksdeutsche soon asked for the area to be returned to German control, but this did not occur. As a result of the transfer of this region, the borders of the NDH then reached to the outskirts of Belgrade. Bulgarian occupation Some parts of Serbia, including Vranje, Bosilegrad, Caribrod and Pirot were occupied by Bulgaria. In January 1942, to secure the railroads, highways and other infrastructure, the Germans began to make use of Bulgarian occupation troops in large areas of the occupied territory, although these troops were under German command and control. This occurred in three phases, with the Bulgarian 1st Occupation Corps consisting of three divisions moving into the occupied territory on 31 December 1941. This corps was initially responsible for about 40% of the territory (excluding the Banat), bounded by the Ibar river in the west between Kosovska Mitrovica and Kraljevo, the West Morava river between Kraljevo and Čačak, and then a line running roughly east from Čačak through Kragujevac to the border with Bulgaria. They were therefore responsible for large sections of the Belgrade–Niš–Sofia and Niš–Skopje railway lines, as well as the main Belgrade–Niš–Skopje highway. In January 1943, the Bulgarian area was expanded westwards to include all areas west of the Ibar river and south of a line running roughly west from Čačak to the border with occupied Montenegro and the NDH. This released the 7th SS Volunteer Mountain Division Prinz Eugen, which had been garrisoning this area over the winter, to deploy into the NDH and take part in Case White against the Partisans. Many members of the Volksdeutsche from Serbia and the Banat were serving in the 7th SS Volunteer Mountain Division Prinz Eugen. This division was responsible for war crimes committed against the peoples of Bosnia and Herzegovina. In July 1943, the Bulgarian occupation zone expanded northwards, with a fourth division, the 25th Division taking over from the 297th Infantry Division in the rest of the territory (excluding the Banat) that did not share a border with the NDH. From this point, German forces only directly occupied