Reports from Ukraine say Dmytro Bulatov, an activist who says he was abducted and tortured for his alleged involvement in Kyiv riots, has left the country for medical treatment in Lithuania.
The development comes as tens of thousands of protesters gathered across Ukraine on February 2 to demand President Viktor Yanukovych step down.
Bulatov, the spokesman for the Automaidan protest group, disappeared on January 22 and reemerged eight days later bearing signs of beatings and possible torture
He had since been kept in hospital in Kyiv under guard from both police and antigovernment demonstrators.
On February 2, Ukrainian authorities granted permission to Bulatov to leave the country for treatment.
The Baltic News Service reported Bulatov had arrived in Vilnius, Lithuania's capital, shortly before midnight and been immediately rushed to hospital.
Earlier in the day on Kyiv's Independence Square, Klitschko told a crowd of some 50,000 protesters that President Yanukovych's resignation followed by elections was the only way out of the crisis.
"Our proposition is the return to the constitution of 2004; division of powers among president, parliament, and government; formation of a new cabinet; and the most important thing for the resolution of these issues are early presidential and parliamentary elections," Klitschko said.
Klitschko also demanded the unconditional release of all protesters arrested in protests since late November.
Both Klitschko and another opposition leader, Arseniy Yatsenyuk, attended the annual Munich Security Conference on February 1 and met with Western officials.
Klitschko told protesters in Kyiv that he had requested "international mediation in our negotiations with Yanukovych."
Yatsenyuk said, "We spoke to our Western partners and told them that we need real financial aid."
Speaking on February 1 at the Munich Security Conference, Klitschko said that the Ukrainian people had shown their will for political change
despite violence against them, and he called on friends of Ukraine in the West to help Ukraine's democratic movement succeed.
Klitschko also said the opposition's goals were to reduce tensions in the crisis and for the government to abandon what he called a path of terror and violence against protesters and free more than 300 people who have been detained.
At a press briefing on the sidelines of the conference, Klitschko blamed Yanukovych for the current crisis, saying there was "just one person who is responsible for all the escalation and who can easily stop this escalation, and that person is the president of Ukraine, Yanukovych. He has absolute power in his hands and he has absolute responsibility for everything that happens in Ukraine also."
Meanwhile, Yanukovych will return to work on February 3 after falling ill late last week, according to information posted on the his official website.
U.S., EU Support
Earlier on February 1, U .S. Secretary of State John Kerry told the annual gathering of global political leaders and defense officials that the Ukrainian people were engaged in a fight for democracy.
"While there are unsavory elements in the streets in any chaotic situation, the vast majority of Ukrainians want to live freely in a safe and a prosperous country and they are fighting for the right to associate with partners who will help them realize their aspirations and they have decided that that means their futures do not have to lie with one country alone and certainly not coerced," Kerry said.
WATCH: Locals Recount Finding Abducted Ukrainian Activist
Kerry added that the United States and the EU stand with the people of Ukraine in their right to make their own decisions.
And he said, "Russia and other countries should not view the European integration of their neighbors as a zero-sum game."
Kerry met with Ukrainian opposition leaders on the sidelines of the conference, a development seen as a major boost to the protest movement. The opposition leaders included Klitschko and Arseniy Yatsenyuk.
Also on February 1, EU President Herman Van Rompuy reiterated that the association deal is still available to Ukraine. "We know time is on our side. The future of Ukraine belongs with the European Union," he told the conference.
Yanukovych's last-minute refusal to sign the deal with the EU in November, apparently under pressure from Moscow, was the spark for the ongoing protest movement in Ukraine.
With reporting by AFP and AP