Tsikhanouskaya was speaking from exile in neighboring Lithuania before an emergency EU summit, due to be held by video conference, to discuss the crisis unfolding in Belarus.
Alexander Lukashenko, the country's veteran leader, has been struggling to contain a wave of mass protests and strikes that pose the biggest challenge to his 26-year hold on power. He denied rigging the August 9 election to secure a sixth term.
Tsikhanouskaya said, speaking in English in a video address, "Mr. Lukashenko has lost all legitimacy in the eyes of our nation and the world."
The opposition politician said she was the rightful winner of the election and wants new elections to be held under some kind of international supervision.
The EU has signaled it will impose sanctions on Belarusian officials it deems responsible for election fraud and a crackdown on protests in which at least two protesters have been killed and thousands detained.
SVIATLANA TSIKHANOUSKAYA: Honorable leaders of Europe, for the second week in a row, my nation is fighting peacefully for its constitutional right to elect its leaders. The August 9th elections were neither fair nor transparent. The results were falsified.
People who went out to defend their vote in the streets of their cities all across Belarus were brutally beaten, imprisoned and tortured by the regime desperately clinging onto power. Hundreds were injured. At least two people lost their lives. This is taking place right now in the middle of Europe.
I call on you not to recognize this fraudulent elections. Mr. Lukashenko has lost all the legitimacy in the eyes of our nation and the world.
Honorable leaders of Europe, I call on you to support the awakening of Belarus. I call on all countries to respect the principles of international law. I call to respect the sovereignty of Belarus and the choice of Belarusian people.