Uta Zapf, head of the Belarusian working group of the Organization for Security and Cooperation in Europe (OSCE), told a news conference in Minsk that it is "extremely important for the election to be fair, for results to be transparent."
Zapf said that some 400 OSCE observers would monitor the 19 March election.
Lukashenka is accused by Western countries of cracking down on opponents, muzzling independent media and rigging elections.
The Belarusian opposition has tried to join forces by choosing independent Alyaksandr Milinkevich as their sole candidate.
Zapf also said the OSCE expects the Belarusian authorities to allow opposition candidates to register. All candidates must be registered by 21 February.