In the summer of 1944 , the Soviet Red Army reached eastern Lithuania . By July 1944 , the area around Vilnius came under control of the Polish Resistance fighters of the Armia Krajowa , who also attempted a takeover of the German-held city during the ill-fated Operation Ostra Brama . The Red Army captured Vilnius with Polish help on 13 July . The Soviet Union re-occupied Lithuania and Joseph Stalin re-established the Lithuanian Soviet Socialist Republic in 1944 with its capital in Vilnius . The Soviets secured the passive agreement of the United States and Great Britain ( see Yalta Conference and Potsdam Agreement ) to this annexation . By January 1945 , the Soviet forces captured Klaipėda on the Baltic coast . The heaviest physical losses in Lithuania during World War II were suffered in 1944 – 1945 , when the Red Army pushed out the Nazi invaders . It is estimated that Lithuania lost 780,000 people between 1940 and 1954 under the Nazi and Soviet occupations
Yalta Conference
Yalta Conference
History of Lithuania