MOSCOW — Maria Kolesnikova, one of three Belarus women who ran the opposition campaign against longtime authoritarian president Alexander Lukashenko, was detained by a group of unknown men and shoved into a van Monday morning, according to independent Belarusian media citing a witness.

Kolesnikova is the only remaining top opposition figure still in Minsk, after the two other women left Belarus in the wake of a disputed election result that has triggered weeks of mass street protests.

Two others figures involved in the Coordination Council, a group of civic leaders set up by the opposition to negotiate a power transition, also disappeared Monday morning, according to the opposition.

“Their whereabouts are unknown,” the council said in a statement Monday, accusing the regime of using methods of terror. “Obviously such methods are illegal and cannot lead to any result other than the aggravation of the situation in the country, a deepening of the crisis and further growth of protests.”

Kolesnikova was dragged into a dark van marked “Connection” and driven to an unknown location, according to local media, a day after plainclothes police chased and beat peaceful protesters in Minsk. An estimated 100,000 people demonstrated against the government on Sunday and more than 630 were arrested, according to police.

Independent Belarusian media, Tut.by, cited a witness who gave her name only as Anastasia who reported she heard the sound of a phone falling and a scuffle at around 10:05 a.m. near the National Art Museum. She saw Kolesnikova seized by several masked plainclothes men and put into the van. Police have denied Kolesnikova was arrested.

With most opposition leaders jailed or out of the country, Kolesnikova was an important rallying point for protests, including mass solidarity marches of women wearing white and red, the colors of the Belarusian republican flag.

Opposition presidential candidate Svetlana Tikhanovskaya left suddenly for Lithuania on Aug. 12, hours after going to the Central Election Commission to lodge a protest of the result. Tikhanovskaya, whose husband, popular blogger Sergei Tikhanovsky remains in prison, has not detailed what happened at the commission that prompted her to leave the country.

Tikhanovskaya confirmed the disappearances on Monday of Kolesnikova, as well as the other two members of the council.

“The kidnapping of Maria Kolesnikova, Anton Rodnenko and Ivan Kravtsov is an attempt to disrupt the work of the Coordination Council. But this will not stop us,” she said.

The third face of the opposition’s presidential campaign, Veronika Tsepkalo, wife of another presidential candidate, fled Belarus shortly after the Aug. 9 election after receiving phone calls warning she would be arrested. Her husband, businessman Valery Tsepkalo who was barred from running, had fled earlier with their two sons, 10 days before the election.

The three women, all stand-ins for their husbands or colleagues who were jailed or barred from running in last month’s presidential election, ran an electrifying campaign that won wide support.

Belarus electoral authorities declared Lukashenko the election winner with 80.1 percent of the vote, compared with just 10.2 percent for Tikhanovskaya — a disputed result that has been rejected by the United States and European leaders and triggered the protests.

Election results were widely condemned as falsified, with some polling stations recording more votes than voters. Some polling station workers came out later stating that they had signed falsified election protocols because they felt afraid or powerless.

Kolesnikova is the campaign manager for opposition candidate Viktor Babariko, a former banker who was jailed by authorities along with his son before the election.

Kolesnikova’s disappearance came two days after another opposition figure, Olga Kovalkova, was evicted from the country Saturday after serving 15 days in jail for protesting. She said officers of the Belarusian internal security, the KGB, told her she had the choice to leave the country or serve a very long jail sentence.

She said she was removed from prison with a hood over her head and forced into a car and kept out of sight. According to Kovalkova, the agents drove her to the Polish border, where they handed her a passport and a certificate that she did not have the novel coronavirus, although she had never taken a test.

“Apparently, they wanted to make sure that people think that I left the country voluntarily, I simply escaped,” she told Echo of Moscow. “They released a story on TV that Tikhanovskaya’s comrade-in-arms had left the country. Only they forgot to mention that they forcibly expelled me.”

Another member of the Coordination Council, Pavel Latushko, who fled Belarus on Sept. 2, told Russian news agency Tass on Monday that authorities gave him the choice of being prosecuted or leaving the country. Two other members of the council, Liliya Vlasova and Sergei Dylevsky, were arrested last month.

Lukashenko, clinging on to power, has taken to appearing in public toting an automatic weapon and issuing dire warnings that NATO is about to invade, comments rejected by NATO leaders.

Isolated and politically besieged, he turned to Russian President Vladimir Putin last month begging for support. Putin, who recently pushed through constitutional changes that could see him rule until 2036, promised to send riot police if necessary.

Moscow has been pursuing economic and political integration with Belarus for decades, given its strategic position bordering NATO countries. The countries signed a union treaty in 1999 but until the current crisis over this political legitimacy, Lukashenko had stalled on integration.