Belarus under Alexander Lukashenko is the last dictatorship in Europe, US President George W Bush said ahead of his arrival in the region for VE Day.
Speaking to Lithuanian television, he said America would work with other states to ensure the next elections in the ex-Soviet republic were free.
Belarus accused the US of meddling in its affairs last month when its top diplomat made similar comments.
Condoleezza Rice met Belarussian dissidents on her visit to the region.
"One of the roles the United States can play is to speak fairly about the need for Belarus to be free... and make sure that the elections are free," Mr Bush told the TV station in Washington.
The next presidential election in Belarus is set for 2006.