On 20 July, the Soviet forces under Marshal Konstantin Rokossovsky forced their way across the Bug River and on that same day the combined meeting of Polish communists from the Moscow and Warsaw factions finalized the arrangements regarding the establishment (on 21 July) of the Polish Committee of National Liberation (PKWN), a temporary government headed by Edward Osóbka-Morawski, a socialist allied with the communists. Gomułka and other PPR leaders left Warsaw and headed for the Soviet-controlled territory, arriving in Lublin on 1 August, the day the Warsaw Uprising erupted in the Polish capital.