'Bilo Gora Ost' was a German and Croat operation against the partisan forces of Josip Broz Tito in the puppet state of Croatia in German-occupied Yugoslavia (25/27 August 1943).

The undertaking’s objective was the destruction of the 16^th and 18^th Brigades of the 12^th Division, estimated at a strength of 2,000 men, in the eastern part of the Bilo mountain region.

The German contribution to the operation was the 1/135^th Reserve-Grenadierregiment of Generalleutnant Hans Freiherr von Falkenstein’s 45^th Division and two battalions of the 14^th SS Polizeiregiment, while that of the Croats was elements of Pukovnik Matija Čanić's 4^th Mountain Brigade, 2^nd Cavalry Group and 37^th Ustase Battalion.

The partisans were found and engaged around the village of Lončarica some 7 miles (11 km) to the south-south-west of Virovitica on 25 August, but during the night escaped the Axis cordon and withdrew to the south-east into the Papuk mountain region. The partisans later claimed that the Axis losses were six men killed, eight wounded and 10 missing, and admitted their own losses of five men killed and 14 wounded.