MINSK, Belarus — One day after President Aleksandr G. Lukashenko of Belarus promised to crush with an iron fist the protests that have broken out since his re-election this month, tens of thousands of people took to the streets of the capital, Minsk, on Sunday to show their determination to force him out of office.
After a week of rallies and publicity stunts in support of Mr. Lukashenko, who has led Belarus, a former Soviet republic, since 1994, many expected the protests against him to ebb. But by late Sunday afternoon, a sea of people had filled the main Independence Avenue in central Minsk, blocking all traffic there and on side streets.
Some estimates put the number of demonstrators at well over 100,000, in what appeared to be a repeat of a similar rally a week earlier.
Although Mr. Lukashenko declared a landslide victory and 80 percent of the vote in the Aug. 9 election, protesters and international bodies, including the European Union, have called it fraudulent. The main opposition candidate, Svetlana Tikhanovskaya, also declared victory and fled to neighboring Lithuania out of fear for her safety.
Initial protests over the results were met with a violent crackdown by Mr. Lukashenko’s robust law enforcement apparatus, including beatings and mass detentions. No arrests or clashes were reported on Sunday, despite the presence of riot police vans parked near the demonstrations, although Mr. Lukashenko told a rally of supporters in the city of Grodno this weekend that protesters had until Monday to calm down.
Many at Sunday’s protest were wrapped in Belarus’s traditional white-and-red flag, which became an opposition symbol after Mr. Lukashenko replaced it with a more Soviet-looking emblem soon after coming to power. A few came with the one used by Mr. Lukashenko’s supporters — a bid to show that the country is united in a desire to see him gone from office.
“It doesn’t matter what flag it is, we just want him to leave,” said Darya O. Rolya, 28, an accountant.
It was unclear how the protesters could achieve that aim, with Mr. Lukashenko having indicated repeatedly that he has no intention of succumbing to pressure from the streets.
“We had elections,” he told a crowd of workers last Monday. “Until you kill me, there will not be any more elections.”
Later Sunday afternoon, a group of protesters moved toward the Independence Palace, Mr. Lukashenko’s vast official residence just outside the center of Minsk. The government deployed armored vehicles and armed army officers to protect the compound, which is surrounded by a tall fence. After approaching the first line of defense, the protesters made a U-turn and went back to the city center.
Mr. Lukashenko observed the protests from a helicopter, at one point calling the demonstrators “rats,” according to a video released by his news service.
Shortly after that, Mr. Lukashenko landed at the palace. A video published online by the news service showed him wearing body armor and holding an automatic rifle as he disembarked the helicopter with his 15-year-old son, Nikolai, in a commando uniform and bearing a rifle too.
Mr. Lukashenko approached riot police officers blocking a nearby street and thanked the men, who shouted, “We are with you until the end,” according to another video.
“We will deal with them,” Mr. Lukashenko told them, in an apparent reference to the protesters.
In the past week, Mr. Lukashenko has pushed to rally his supporters around the flag. He made a flurry of statements about an imminent invasion from the West and an internal conspiracy to destabilize Belarus. He accused protesters of being against Russia — a key ally — and called them “rats” and “trash.” On Sunday, some protesters waved the Russian flag to show that they do not want their country to turn away from Moscow.
Some of Mr. Lukashenko’s assertions seemed directed at the attention of President Vladimir V. Putin of Russia, who is leery of any anti-Russian protests in former Soviet republics. On Saturday, Mr. Lukashenko thanked Mr. Putin and called him a friend, one day after confirming having invited several Russian journalists to replace the Belarusian ones who resigned from state-run news media outlets this month in protest over censorship.
Some protesters said that they had achieved a significant feat by exceeding the turnouts at Mr. Lukashenko’s rallies, but that it would be hard to put more pressure on the president.
One of them, Aleksandr I. Potekhin, said the protests needed a leader.
“By itself, a crowd of people cannot achieve much,” said Mr. Potekhin, 30, a construction engineer. “I feel that something more radical is required to achieve our aims, but people are afraid to do that.”
“This situation forces us Belarusians to unite,” said Igor Y. Andryushko, 37, a worker at Minsk Tractor Works, one of the main sites of the worker protests. “I don’t want it to take a violent turn. I think everything will end peacefully.”