MINSK, Belarus — The popular uprising against President Aleksandr G. Lukashenko of Belarus entered a new phase on Friday as protests spread at the state-run factories at the core of his political base.
In one of the most dramatic demonstrations, hundreds of workers gathered at the entrance to the Minsk Tractor Works, a Soviet-era industrial giant whose farming machinery is one of Belarus’s best-known brands. They presented an ultimatum to management: Unless a new and fair election is called, they will go on strike.
“We refuse to go back to work,” said one of the workers, Sergei A. Drilevsky, 35. “People refuse to have this president. He is illegitimate.”
Footage of similar protests by transit workers and autoworkers, at an oil refinery, and at factories making synthetic fabric, fertilizer and trucks coursed through social media. The new flash of discontent at state-owned companies — making it clear that the opposition to Mr. Lukashenko has spread far beyond the urban middle class — appeared to have been driven by accounts of widespread police violence against protesters that spread online on Thursday.
“These people were worse than the Nazis,” said Anatoly I. Los, 58, head of the electroplating workshop at the Minsk Tractor Works. “We cannot live like this anymore.”
The coming days will be critical for Mr. Lukashenko, as the authoritarian long known as “Europe’s last dictator” tries to cling to power in the face of the biggest popular challenge to his 26 years of rule. His government offered conciliatory gestures on Friday, pledging to release detained protesters, but also making it clear that Mr. Lukashenko had no plans to bend to their demands: The Central Election Commission announced finalized results of last Sunday’s presidential election, which critics saw as blatantly rigged.
Mr. Lukashenko garnered 80 percent of the votes, the commission said, compared with 10 percent for Svetlana G. Tikhanovskaya, the former stay-at-home mother who has emerged as the opposition leader.
Ms. Tikhanovskaya, who supporters say was forced to leave the country for Lithuania on Tuesday, called for new protests this weekend. She described herself as the true victor in the election, called for dialogue with the authorities and said she was forming a “coordination council to assure the transfer of power.”
“Belarus will never again want to live under its previous rulers,” she said in a video message. “Most people do not believe in their victory.”
Mr. Lukashenko appeared to be still in control of his country’s military and powerful security services, but his position has weakened in recent days. A turning point came Thursday, when detained protesters emerged from jails with grisly wounds and tales of brutal beatings and overcrowded cells.
The police violence gave fresh impetus to a move that some protest organizers had been calling for on social media all week, initially with little success: a general strike. The protests by factory workers pose a particular risk to Mr. Lukashenko because state-owned companies generate more than half of the country’s industrial output. Keeping Soviet-era industrial behemoths out of the hands of business tycoons has been a point of pride for Mr. Lukashenko, a sharp contrast to the “oligarchs” who took over much of the economy in neighboring Russia and Ukraine.
Outside the Minsk Tractor Factory, workers said that the situation was Mr. Lukashenko’s own doing. They said they were enraged by law enforcement attacks on peaceful protesters, demanded that all detained demonstrators be released immediately and that riot police be removed from the streets.
About half of the workers at the factory had walked off the job, Aleksei V. Pavlovich, a paint shop worker, said Friday. More than 15,000 people work at the factory, one of the world’s largest producers of agricultural equipment.
Vitaly M. Vovk, the factory’s manager, tried to calm people down, but was booed after he called what was happening an unsanctioned rally. He said that the workers’ demands were political and that he could pass them on only to high-ranking members of the Belarusian government.
Later, Belarus’s prime minister, Roman A. Golovchenko came to the factory to speak to the workers, Mr. Drilevsky said.
“After he refused to respond to our questions in front of the media, we decided to start marching toward the main government building,” Mr. Drilevsky said in a phone interview. Photographs showed hundreds of tractor factory workers marching toward the center of the city.
Workers at other factories in Minsk and across the country were also considering striking. There was a mass gathering at the Minsk Automobile Plant on Friday, workers coming out of the factory said.
After the widespread police violence earlier this week, the authorities pulled back and allowed peaceful protests across the country on Thursday. The streets of Minsk on Friday were full of people marching with flowers and waving to passing cars.
Some senior officials sounded conciliatory notes; the top law enforcement official, Interior Minister Yuri K. Karayev, apologized to those “caught in the middle” of what he described as a justified police response to violent protests.
The Interior Ministry also said it was working as fast as possible to address overcrowding in detention centers, and that 2,000 people had already been released.
Mr. Lukashenko played down the strikes’ size in a televised meeting with officials from the construction industry that was broadcast on Friday, but he warned that the job actions would benefit Belarus’s economic competitors in Russia and in the West if they continued. He opened the meeting with an irritated-sounding attempt to pierce rumors of his imminent demise.
“For starters: I’m alive for now, and I haven’t left the country,” he said.
Ivan Nechepurenko reported from Minsk, and Anton Troianovski from Moscow.