Belarusian opposition figures say police detained two opposition politicians as protesters held a third day of rallies against Sunday's re-election of President Alexander Lukashenko.
They say the two senior members of the United Civil Party were detained early Tuesday in the capital, Minsk.
At least 400 opposition activists set up a tent camp in the city's October Square late Monday. They vowed to hold a round-the-clock vigil, despite freezing temperatures.
Sunday's landslide election victory by Mr. Lukashenko has been condemned as a fraud by the West.
Belarusian election officials say Mr. Lukashenko won 83 percent of the votes Sunday, while Mr. Milinkevich won six percent.
Mr. Lukashenko dismissed his opponents Monday, saying their attempts to spark a "revolution" had failed.
Belarusian opposition groups are hoping to repeat the success of peaceful revolutions in Ukraine and Georgia in recent years.
Belarusian opposition leader Alexander Milinkevich visited the square during the night and promised to stand by the protesters until they achieve victory. Supporters tried to bring them blankets, food and hot drinks, but some were blocked by police. Mr. Milinkevich is demanding a free and fair revote.
European election monitors say Sunday's vote was marred by intimidation and widespread arrests of opposition supporters. The European Union External Affairs Commissioner Benita Ferrero-Waldner says new sanctions against Belarus are "very likely."
A U.S. State Department spokesman Sean McCormack called election conditions in Belarus "appalling." He says Washington is preparing to take serious measures against those responsible for fraud and human rights abuses.
But Russian election observers say the voting was fair and transparent. President Vladimir Putin has congratulated Mr. Lukashenko on winning a third term.
Mr. Lukashenko has wide support among many elderly and rural Belarusians who believe he has kept the country stable after the collapse of the Soviet Union.
But the United States calls him Europe's last dictator because of his suppression of human rights and free speech.