Ukraine's President Petro Poroshenko has called elections being held in the rebel-held east of the country illegitimate.
He said that Ukraine and the rest of the world would reject the results, and called on Russia to do the same.
Ukraine's curiously named Internet Party has come up with an offbeat campaign gimmick to lure voters - dressing as Star Wars characters.
Tensions remain high in eastern Ukraine after at least three died in a day of shooting during what was supposed to be an Easter truce.
In an exclusive interview with NBC News, the Ukrainian Prime Minister warns of the dangers of unchecked Russian expansion and aggression.