A "significant" number of Russian troops have now withdrawn from Ukraine, a Nato spokesman said.
Lieutenant-Colonel Jay Janzen told Reuters: "There has been a significant pullback of Russian conventional forces from inside Ukraine, but many thousands are still deployed in the vicinity of the border.
"It is difficult to determine the number, as pro-Russian separatists control several border crossings and troops are routinely moving back and forth.
"Further, Russian special forces are operating in Ukraine, and they are difficult to detect."
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.