Initially, Guderian's forces advanced almost unopposed. However, on 14 September, they were stopped in the area of Brześć Fortress and Kobryn by a four-battalion-strong improvised force under General Konstanty Plisowski. In the three-day-long battle, which became known as the Battle of Brześć Litewski, both sides suffered significant casualties. Although the Poles finally withdrew from the area on 17 September, the Germans did not start the pursuit soon enough to rout the retreating Poles. The simultaneous attack on Kobryn, which is sometimes referred to as the Battle of Kobryń, was inconclusive, with the Polish improvised 'Kobryń' Infantry Division under Colonel Adam Epler withdrawing unopposed.