Belarus activists describe dramatic alleged abduction and last sighting of Maria Kolesnikova

At a lengthy press conference in the Ukrainian capital, activists Ivan Kravtsov and Anton Rodnenkov gave their version of their disappearance. It began, they said, with a trip to check on the safety of their colleague Maria Kolesnikova, a prominent anti-government activist who has been detained by the Belarus Border Control.

All three are members of the Belarus Coordination Council, the country's main political opposition group, which seeks to coordinate a peaceful transition of power in the wake of August's disputed elections.

Rodnenkov said he and Kravtsov visited Kolesnikova's home in Minsk on Monday after hearing reports that she was missing.

When the two men arrived at her home, however, they were pushed into a bus by unidentified men and interrogated, they told reporters. They were later put separately in a convoy of five or six cars -- including Kravtsov's BMW -- and driven to the Belarusian border with Ukraine.

Rodnenkov said the convoy halted in the no-man's land between the two borders. He said he was then told to get into Kravtsov's car -- where he saw Kravtsov sitting in the passenger seat -- and noticed that all three passports were in the vehicle.

"At that moment Maria appeared," Rodnenkov said.

Kolesnikova was "forcefully pushed" into the backseat of a car with them, he said, but resisted being sent to Ukraine. Seeing her passport, she tore into pieces and "threw them out of the window to the unknown people that surrounded the car," Rodnenkov said.

Kolesnikova then climbed out through the car's window, and began walking back toward the Belarusian border, he said. Belarusian officials confirmed Tuesday on state television that she was detained by Border Control.

Meanwhile, Rodnenkov "hit the gas pedal" and gunned it for Ukraine.

According to the men, the Belarusian authorities gave chase and tried to block their way with a bus, but they managed to reach the safety of the Ukrainian side of the border where they "were greeted by very amiable and understanding servicemen of Ukrainian border control."

CNN cannot confirm all the details of their experience. However, Belarusian Border Control has confirmed that the Kravtsov and Rodnenkov entered Ukraine at 4 a.m. on Tuesday.

They are currently the last people to report seeing Kolesnikova since Monday.

US 'deeply concerned' by reported abduction

Reports that the trio were missing emerged this week after a fourth consecutive weekend of anti-government protests in the country. Unrest erupted in Belarus shortly after President Alexander Lukashenko claimed victory in the August 9 election, which observers have criticized as neither free nor fair.

Lukashenko, who has ruled for 26 years and is often described as Europe's last dictator, remains defiant despite the mass demonstrations.

His rival, the main Belarusian opposition candidate and Coordination Council leader Svetlana Tikhanovskaya, has fled the country. Her confidante, Olga Kolvakova, was forced to leave Belarus for Poland over the weekend, according to a council statement.

Speaking from Vilnius, Lithuania, Tikhanovskaya said in an interview with CNN's Christiane Amanpour on Monday, "at the moment, members of the Coordination Council I created are chased, kidnapped and harassed. And it's worrying me a lot, because at the moment we still don't know where Maria Kolesnikova is."

US Secretary of State Mike Pompeo said in a statement released Tuesday evening that the US is "deeply concerned by the reported abduction" of Kolesnikova, Rodnenkou and Krautsou, and the "attempted forced expulsion" over the border to Ukraine.

He said the US is considering additional targeted sanctions and emphasized that authorities in Belarus are responsible for the safety of Kolesnikova and "all those unjustly detained."

"We call on the Belarusian authorities to end the violence against their own people, release all those who have been unjustly detained, including U.S. citizen Vitali Shkliarov, and engage in meaningful dialogue with genuine representatives of Belarusian society," he said.

The European Union on Monday condemned Kolesnikova's detention and that of all political activists in Belarus, criticizing the "intimidation" of Belarusian citizens.

EU High Representative for Foreign Affairs Josep Borrell called for the release of Kolesnikova and all political activists, including 633 anti-government protesters who were arrested after a peaceful march on Sunday.

"It is clear that the state authorities in Belarus continue to intimidate or allow intimidation of its citizens in an increasingly lawless way and crudely violate both their own domestic laws and international obligations," Borrell said.

Russia, in contrast, has refused to acknowledge the presence of political prisoners in Belarus.

Speaking on a conference call with journalists, Kremlin spokesman Dimitri Peskov said Tuesday, "We do not yet have detailed information about what happened to (Maria Kolesnikova)," and warned against leaping to conclusions.

"On the whole, we are not ready to admit the existence of political prisoners in Belarus," Peskov said.