While the treaty was being negotiated and signed, most of the territory granted by the treaty to Lithuania was already controlled by Bolshevik forces. As the Poles were retreating from western Russia, Lithuania attempted to secure the borders outlined in the treaty. Lithuanian forces crossed the Foch line on July 19, seeking to take control of the territories granted to Lithuania by the Soviet Union, advancing rapidly despite Polish protests and, in several cases, fighting skirmishes with the retreating Polish forces. That led to clashes in southern Lithuania over the towns of Sejny, Augustów and Suwałki. According to historian Piotr Lossowski, the Lithuanians also provided the Soviets with logistical support.