Unidentified people reportedly detain Maria Kolesnikova in central Minsk as police arrest demonstrators.

Belarusian protest leader Maria Kolesnikova has been abducted by unidentified individuals in central Minsk, according to the Belarusian Tut.By media outlet, citing a witness.

Masked men took her and drove off in a minivan, said Tut.By.

The development on Monday came hours after security forces arrested 633 protesters following a mass anti-government rally on Sunday, the latest since the disputed August election.

Police in Minsk said they had not arrested Kolesnikova, according to Russia's Interfax news agency.

Kolesnikova is the last one left in Belarus of three female politicians who joined forces before the August 9 presidential election to challenge longtime leader Alexander Lukashenko.

A vocal critic of Lukashenko, she has played an important role in the country's post-election political crisis, which has seen weeks of mass protests and strikes by people who accuse the strongman of rigging his re-election, something he denies.

Before the vote, Kolesnikova teamed up with opposition presidential candidate Svetlana Tikhanovskaya who later fled to Lithuania, and with Veronika Tsepkalo, who has also since left the country.

Another leading activist, Olga Kovalkova, arrived in Poland on Saturday, saying she had been told she would face arrest if she stayed in Belarus.

Tsepkalo told Al Jazeera from Poland that her allies in Belarus still did not have any information on Kolesnikova's whereabouts.

"Hopefully she will be released as soon as possible. I really worry about her," she said.

Tsepkalo also said it was "not safe right now for the leaders and as you can see all the leaders are put in prison, detained or had to leave the country". 

"Lukashenko isolates the strongest leaders. During this presidential season, he has put two opposition leaders in prison. My husband is facing up to 15 years behind bars on criminal charges," she said.

Tsikhanouskaya said the reported abduction of Kolesnikova looked like an attempt by authorities to derail the opposition's Coordination Council and intimidate its members.

The economy

Earlier on Monday, central bank figures showed Belarus had burned through nearly one-sixth of its gold and foreign exchange reserves, or $1.4bn, in August, as it fought to prop up its rouble currency during the wave of unrest.

Kolesnikova had announced on August 31 that she was forming a new political party, Together, with the team of jailed opposition figure Viktor Babaryko with whom she had previously worked.

On Sunday, columns of protesters defied a government warning not to march, waving red-and-white opposition flags and shouting "go away" and "you're a rat".

Protests also took place in major cities throughout Belarus.

Lukashenko has been in power since 1994 and, buoyed by a show of support from traditional ally Russia, has rejected calls for new elections.

Unprecedented protests broke out when he claimed he had been re-elected with 80 percent of the vote.

Daragh McDowell, principal analyst at the global consulting firm Verisk Maplecroft, said economic factors are playing a significant role in the demonstrations, with the country "rapidly running out of money". 

"The IT sector has been repeatedly undermined with the internet shutdowns to disrupt the protesters. We've also seen a lot of strikes in the state-owned sector as well. So the Belarussian economy is really on the brink," McDowell told Al Jazeera.

"The people have lost their fear of Lukashenko, he's lost a lot of his authority. No matter how many riot police he's deployed to the streets, it just hasn't stopped people from continuing to come out."