254. ваздухопловни ловачки пук на Белградском аэродроме
It isn't Soviet VVS 254 iap, it is Yugoslav Air Force 254 fighter regiment. Regiment was formed in Soviet Union as 1-й Югославский истребительный авиационный полк in October 1944.
Obviusly planes had just arrived from SSSR and still have Soviet markings.
