The US and EU have condemned elections in Belarus which international monitors say were severely flawed.
Opposition supporters again took to the streets of Minsk on Monday
Fresh protests were held in Belarus on Monday, a day after President Alexander Lukashenko won 82.6% of the vote.
The White House, which has previously labelled Mr Lukashenko a dictator, says it does not accept the results. The EU says it is likely to impose sanctions.
Mr Lukashenko denounced the statements as "foreign pressure", while Russia - a key ally - sent him congratulations.
Main opposition candidate Alexander Milinkevich has described Mr Lukashenko as an "illegal, illegitimate president".
Thousands of supporters heeded his call and turned out in the capital, Minsk, on Monday night, but it appeared their numbers were only about half Sunday's crowd of 10,000.
"Our protest will be strong and long," Mr Milinkevich told the crowd, urging them not to disperse.
"We will never recognise this election. It's not an election but an anti-constitutional seizure of power."
A number of protesters set up tents at the scene, but most demonstrators were later reported to have dispersed.
A large presence of riot police was also on the streets, the Associated Press news agency reported.
Official figures say the election had a turnout of 92.6%. The result gives the president, in power since 1994, a third term in office.
However the OSCE, Europe's main election monitoring body, said there had been harassment and detention of opposition activists, biased media coverage and obstruction of independent monitors.
"The Belarussian election was severely flawed due to arbitrary use of state power and restrictions to basic rights," the OSCE said in a statement.
In the US, White House spokesman Scott McClellan said the US was backing opposition calls for a re-run of the election.
"The United States does not accept the results of the election," Mr McClellan said.
"The election campaign was conducted in a climate of fear. It included arrests and beatings and fraud."
Austria's Foreign Minister Ursula Plassnik, representing Austria's presidency of the EU, said in Brussels that the vote was marred by a "climate of intimidation".
And EU External Relations Commissioner Benita Ferrero-Waldner said some sort of action against Belarus - possibly diplomatic sanctions - was now "very likely indeed".
Earlier a rival observer mission, from the Russian-led Commonwealth of Independent States, said the election was open and transparent.
And Russian President Vladimir Putin told Mr Lukashenko in a message quoted by the Kremlin: "The results of the election demonstrate the confidence of the electorate in your policies."
Mr Lukashenko, in a television appearance on Monday, insisted that the poll was fair and democratic and called the complaints about it "absurd".
Alexander Lukashenko: 82.6%
Alexander Milinkevich: 6.0%
Sergei Gaidukevich: 3.5%
Alexander Kozulin: 2.3%
"Despite the unashamed foreign attempts to dictate to us and colossal external pressure, they have failed to break us," he said.
Mr Milinkevich has called for continuing demonstrations, following a protest by about 10,000 people on Sunday.
"In Belarus, we did not have an election but an unconstitutional seizure of power," he said in a news conference broadcast across Belarus.
"I very much ask all to come out into the square today, in as large numbers as possible. I believe that Belarussians have awakened, overcome fear and can stand up for their future."
But the BBC's Emma Simpson, in Minsk, says there has been no evidence so far of any Ukrainian-style Orange Revolution.
Mr Lukashenko has warned he will not tolerate any attempt at a "coup", while police say protesters "trying to destabilise the situation" will be treated as terrorists and could face the death penalty.
But our correspondent says that despite his authoritarian regime, Mr Lukashenko has genuine popular support, particularly in rural areas.