By MICHAEL SCHWIRTZ
MOSCOW - In what appears to be another step in suppressing criticism and dissent, Belarus asked the Organization for Security and Cooperation in Europe to leave the country after its election monitors accused the government of fraud in the presidential election last month.
A spokesman for the Belarussian Foreign Ministry announced the decision on Friday evening, saying that the group had fulfilled its mandate and that it was no longer needed.
"This was a conscious decision due to the absence of an objective basis for retaining the O.S.C.E. mission in Belarus," the spokesman, Andrei Savinykh, said, according to Belarussian news agencies.
The organization, which has maintained an office in the capital, Minsk, since 1998, criticized the decision. Its chairman, Audronius Azubalis, the foreign minister of Lithuania, expressed "deep regret" over the move.
"Its mandate has not been completed," Mr. Azubalis said in a statement posted to his ministry's Web site. "There is an important job for the O.S.C.E. to continue in Belarus."
The group's monitors had detailed widespread fraud in the election, in which the country's longtime authoritarian president, Aleksandr G. Lukashenko, won about 80 percent of the vote, according to official tallies.
The organization has also strongly condemned the violent police crackdown on thousands of antigovernment demonstrators who gathered in Minsk after the election to protest the results. At least 600 people were arrested.
Ties between the West and Belarus, a former Soviet republic, had been improving in advance of the election, as the government allowed for at least a semblance of a campaign. But that window shut after the election.
Mr. Lukashenko, who has been in power for 16 years, responded angrily to the criticism and vowed to do away with what he described as "mindless democracy."
His government has also cracked down on the news media, raiding the offices of independent journalists and shutting down an opposition Web site that had been one of the main sources of independent information.
Arrests of opposition figures have continued almost daily. Five former presidential candidates have been charged with fomenting unrest after the election and could face up to 15 years in prison. Many of their associates have also been arrested or gone into hiding. "Continued positive engagement with Mr. Lukashenko at the moment seems to be a waste of time and money," the foreign ministers of Sweden, the Czech Republic, Poland and Germany said in a recent article on the op-ed page of The International Herald Tribune.
Russian leaders, who in recent years have clashed with Mr. Lukashenko, have avoided criticizing him in the wake of the elections. Russia's president, Dmitri A. Medvedev, congratulated Mr. Lukashenko on his victory and expressed hope for continued friendly relations.