Saakashvili, writing in the "International Herald Tribune" newspaper, said he expects the election to be "a mass exercise in ballot fixing."
He said Europe's reaction will "test the continent's resolve to rid itself of dictatorship."
Former Czech and Polish presidents Vaclav Havel and Lech Walesa have also urged the world to give its full support to the opposition.
Saakashvili also urged the EU to impose stricter economic and political sanctions on the government of President Alyaksandr Lukashenka, who is running for a third term in the election.
The Belarusian KGB on March 16 said protests would be viewed as terrorism.
(with material from Reuters, AFP)
MEET THE CANDIDATES: Read brief biographies of the four candidates in the March 19 election.