France, Germany and Poland have pointed out the that the election is taking place with no observers from the Organization for Security and Cooperation in Europe and the Council of Europe.
France, Germany and Poland have called on Belarusian President Alexander Lukashenko to ensure a "free and fair" election in the former Soviet republic as fears of irregularities mounted.
Foreign ministers from the three EU nations released a joint statement on Friday deploring the absence of observers from the Organization for Security and Cooperation in Europe (OSCE) and the Council of Europe.
"We urge the Belarus authorities to conduct the presidential election in a free and fair way, especially by ensuring independent surveillance of the vote by local observers," Jean-Yves Le Drian, Heiko Maas and Jacek Czaputowicz said in the statement.
The OSCE's absence will be the first for a national election in Belarus since 2001, due to the lack of an invitation from the government.
The results of the last four presidential elections were not recognised as fair by OSCE observers.
Reports of electoral irregularities
The foreign ministers also pointed to reports of electoral irregularities in early voting for those who will not be able to go to the polls on Sunday.
Lukashenko has ruled over the ex-Soviet country wedged between Russia and Europe with an authoritarian grip for 26 years and has cracked down on an emboldened opposition in the lead-up to the election.
His leading rival, 37-year-old Svetlana Tikhanovskaya, is running in place of her jailed husband and has drawn massive crowds at rallies across the country in an unprecedented display of frustration with Lukashenko's rule.
The three foreign ministers called for the release of prisoners detained for political reasons, and urged the government to refrain from any violence or violations of "civil and political freedoms".
They also warned against a further deterioration of EU-Belarus relations, after "a difficult but promising dialogue" in recent years.
Putin-Lukashenko agree further talks on detained Russians
Belarusian President Lukashenko and his Russian counterpart Vladimir Putin expressed confidence on Friday that tensions over the 33 Russian citizens detained in Minsk last month can be resolved, the Kremlin said.
The arrests further strained relations between the two traditional allies, already soured this year by a dispute over oil.
The group of suspected Russian mercenaries were accused of plotting to foment unrest. Russia has said the men were employees of a private security firm and were passing through Belarus on their way to Latin America.
In a telephone call, the two leaders agreed to determine why the Russians were arrested, find the people responsible and bring them to justice, Lukashenko's press office said.
It added that Putin had noted the importance of Russia and Belarus having "brotherly" relations.
Lukashenko on Thursday said there was a "hybrid war" against Belarus and that the country should expect "dirty tricks" from any side.
EU calls for activists' release
EU foreign policy chief Josep Borrell on Friday called on Belarus, to ensure fundamental freedoms of expression and peaceful assembly and to guarantee candidates' full political rights.
"The country's sovereignty and independence can only be strengthened by peaceful, free and fair elections," Borrell said in a statement.
He also urged Belarusian authorities to immediately release all activists, human rights defenders, bloggers and journalists detained on political grounds.