By MICHAEL SCHWIRTZ
MINSK, Belarus - Heavily armed riot police tossed stun grenades and battered opposition activists with truncheons on Sunday night here as they broke up a gathering to protest the conduct of Belarus's presidential election.
Supporters carried the presidential candidate Vladimir Neklyayev to his campaign headquarters on Sunday after he and others were beaten by riot police during a rally in Minsk.
The violence erupted without warning as a group of 100 or so supporters of an opposition candidate was walking peacefully toward a central square in Minsk, the capital, where several candidates were planning to hold a united demonstration against the Belarus president, Aleksandr G. Lukashenko.
Mr. Lukashenko, often referred to as Europe's last dictator, had earlier in the day suggested that the authorities would take steps to ensure that the opposition would not be able to gather to protest the results. He is expected to easily win another term, after balloting that his rivals maintain was not free and fair.
On Sunday night, Vladimir Neklyaev, an opposition candidate, was leading his supporters on a march to the central square when scores of riot police arrived, tossed stun grenades and began attacking people.
A reporter and a photographer for The New York Times were among those beaten up, but they were not seriously injured. The police slammed people to the ground and held them there for several minutes, pushing their heads into the snow, before suddenly leaving.
Mr. Neklyaev appeared to have been knocked unconscious in the assault and was carried back to his campaign headquarters by his supporters.
It did not appear that other opposition candidates were targets of the riot police on Sunday night, and several thousand people were able to gather on the square for the demonstration.
Earlier in the day, even before the polls had closed in the presidential election, Mr. Lukashenko's rivals said the police were conducting a crackdown to prevent an anti-government demonstrations.
Opposition activists complained that several of their colleagues had been arrested by mid-afternoon, though under what pretext was unclear. Julia Rymashevsky, a spokeswoman for Mr. Neklyaev, one of nine opposition candidates, said at least two campaign aides had been arrested, including one who seemed to just disappear.
"He called a taxi and left his apartment, but he never made it to the taxi," Ms. Rymashevsky said.
Opposition leaders have vowed to protest what they say will inevitably be a fraudulent election. Few here have much doubt that victory will go to Mr. Lukashenko, who has never lost in 16 years as ruler of this former Soviet-republic. Independent monitors have never considered elections here much more than farce.
The authorities had warned opposition leaders to call off their protest and vowed to prevent any of them from gathering after polls closed Sunday evening.
"Don't worry," Mr. Lukashenko said, after casting his vote at a large athletic complex on Sunday. "There will be no one on the square tonight."
The rising tensions on election night belied a concerted attempt by Mr. Lukashenko to make these elections appear more democratic in an effort to court the West amid increasingly sour and unpredictable relations with his longtime patron, the Kremlin.
After a meeting with Mr. Lukashenko last month, the foreign ministers of Poland and Germany said that the European Union could be willing to give Belarus $3.5 billion in aid, but only if the elections were deemed free and fair.
And so, with his country reeling under the stresses of the financial crisis, Mr. Lukashenko seemed to be softening his stance toward his opponents.
Ahead of these elections, opposition candidates received free airtime on national television and had been largely allowed to campaign across the country, though not without the occasional harassment by the local police.
For the first time, candidates were permitted to hold televised debates. Mr. Lukashenko did not participate, though other candidates were able to criticize the president free of censorship live on government-controlled television.
Mr. Lukashenko's government maintains complete control over the vote count, with opposition figures making up less than 1 percent of local commissions tasked with providing the final tally. The president also received nearly 90 percent of all news coverage during the campaign, according to election monitors, who also expressed concern that ballots cast during a five-day early voting period could be tampered with.
"There have been certain improvements in a number of areas," said Jens-Hagen Eschenbaecher, a spokesman for the election-monitoring wing of the Organization for Security and Cooperation in Europe. "But this was not enough to create an even playing field for all candidates during this campaign."
For those campaigning for the opposition out in the snow-bound streets of Minsk recently, there was little question of who had the advantage.