RFE/RL's Belarus Service reports that the women, who were found in the Yelsk district of the country's southeastern Homel region, were taken to a local hospital for medical examinations. They are now said to be at a local police station.
A correspondent for the Belarusian news agency Belapan reported that doctors observed bruises on the women's hands and other parts of their body.
The women told journalists at the scene that on the evening after their protest on December 19, they were at a Minsk bus station when six men abducted them and brought them to a forest far from the capital.
They repeated details about their ordeal that Femen's leader, Anna Hutsol, had told RFE/RL earlier in the day from Kyiv.
"They are alive but not in good health. They are very scared," Hutsol said. "They drove them around in a car all night, then brought them to the woods, poured oil on them, threatened to set them on fire, threatened them with a knife, cut their hair with a knife, videotaped everything, and then left them in the woods."
Hustol identified the three women as Aleksandra Nemchinova, Oksana Shachko, and Inna Shevchenko and said the KGB seized their documents.
Aleksei Emelyanenko, a spokesman for the Ukrainian Embassy in Minsk, told RFE/RL that the women's identities could not immediately be confirmed. "We hope to be able to return them to Ukraine soon and from our side, we will continue to follow their situation," he said.
See the latest coverage by RFE/RL's Belarus Service (in Belarusian)
Earlier in the day, Kyiv sent its embassy consul in Minsk to the region to investigate the story. He later met with the activists.
RFE/RL's Belarus Service spoke to people in Byaki, the village where the women were found. They said the women told them that after being terrorized in the woods, their captors had brought them to the nearby border with Ukraine and ordered them to cross it. The women instead made their way to the village, where a local resident took them in.
A man who gave his name as Yuri told RFE/RL that he had lent the activists his mobile phone so they could reach Hutsol.
The Belarusian authorities have not publicly commented on the women's allegations.
But earlier on December 20, Ukrainian Foreign Ministry spokesman Oleksandr Dikusarov told RFE/RL that officials in Minsk said no one had detained the activists and the women had left the city voluntarily.
Femen, which claims to have hundreds of members and thousands of supporters, formed in 2008 to protest discrimination against women in what the group describes as Ukraine's patriarchal post-Soviet society.
Its members' signature strategy of protesting topless has earned the group admiration and ridicule, and no shortage of headlines.
The group's agenda has expanded from protesting domestic inequalities to championing international causes.
In June, Femen activists wore hijabs, the traditional Muslim head scarf, but nothing on top, at a protest in front of Kyiv's Saudi Arabian Embassy over Riyadh's ban on women drivers. They've also stopped traffic in Zurich and caused a stir at the Vatican.
Earlier this month, Femen attempted to stage a protest in Moscow before Russia's parliamentary elections, but were quickly overpowered by security guards.
On December 19, the first anniversary of Belarus's disputed presidential election, the activists gathered in front of the KGB headquarters in Minsk to express solidarity with the demonstrators, politicians, and journalists who were detained in the ensuing protests and government crackdown.
Bare-chested and wearing fake Lukashenka-style mustaches, the women held placards that read, "Freedom to political prisoners" and "Long live Belarus," a mantra of the protest movement.
One Femen member painted a red star on her stomach and partially shaved her head in imitation of Lukashenka's receding hairline.
Several journalists were arrested while attempting to cover the group's demonstration.
Not In Ukraine Anymore...
While Femen's activities are largely tolerated in Ukraine, all signs of dissent are quickly quashed under the Lukashenka regime.
To intimidate activists and protesters, security forces have used tactics similar to what FEemen says happened to its three members.
Ukrainian human rights activist Yevhen Zakharov told RFE/RL that if the group's claims are confirmed, those responsible must be held accountable.
"If this information is confirmed and it is in fact torture [used against Femen activists in Belarus], then Ukraine should demand the punishment of the law-enforcement officers responsible for it. If that is not done, then measures of diplomatic pressure should be taken against Belarus. In my view, this cannot be left without a response," he said.
Hutsol, meanwhile, pledged to take matters into her own hands if necessary. "We'll do everything to have the Belarusian ambassador to Ukraine deported from here," she said from Kyiv. "If he doesn't leave tomorrow, we'll take him to the woods ourselves and shave his head."
Written by Richard Solash, based on reporting by RFE/RL's Belarus and Ukrainian services