Romania and Bulgaria
In August 1944 the 3rd Ukrainian Front engaged in the Iassy-Kishinev Offensive, which resulted in the release of all the Moldavian SSR, and Romania declaring war on Germany.
On 8 September Soviet troops entered the territory of Bulgaria and by the end of the month occupied the country. From 28 September - 20 October 1944 3rd Ukrainian Front in collaboration with the People's Liberation Army of Yugoslavia with the participation of troops of the Fatherland Front in Bulgaria carried out the Belgrade Offensive, which resulted in the liberation of the capital of Yugoslavia, Belgrade, and most of Serbia.
In October 1944 - February 1945, the 3rd Ukrainian Front had forces involved in the Siege of Budapest, including 46th Army. Its troops crossed the Danube and seized a bridgehead on its right bank. In January 1945, they repelled the enemy counter-attacks, trying to relieve the forces surrounded in Budapest, and in March, during the German Operation Frühlingserwachen, a counter-offensive broke the German troops in the area of Lake Balaton. The successful completion of this battle made possible the beginning of the Vienna Offensive on 16 March, in conjunction with the left wing 2nd Ukrainian Front. Thereafter the front's forces completed the liberation of Hungary, expelled the enemy from the eastern part of Austria and took its capital, Vienna.
On 15 June 1945, the on the basis of a Stavka directive on May 29, 1945 the front was disbanded, and reorganised as the Southern Group of Forces. 26th Army was grouped with 37th Army into the SGF.
The Front included 57th Army from October to December 1944.
Read more about this topic: 3rd Ukrainian Front