The US Secretary has decried what he calls a "disturbing trend" of governments in central and eastern Europe, including in Ukraine, trampling the ambitions of ordinary people.
"The aspirations of citizens are once again being trampled beneath corrupt, oligarchic interests," John Kerry said in Munich, where he met with Ukrainian opposition members on the sideline of an international security conference.
Kerry said the crisis in Ukraine is about ordinary people fighting for the right to associate with the European Union, adding that Ukrainians have decided their futures don't have to lie with one country.
Nowhere is the fight for a democratic, European future more important today than in Ukraine
"Nowhere is the fight for a democratic, European future more important today than in Ukraine," he said. "While there are unsavory elements in any chaotic situation, the vast majority of Ukrainians want to live freely in a safe, prosperous country."
The US and Russia have attacked each other at a security conference in Munich over Ukraine's future as key opposition figures met US Secretary of State John Kerry on the sidelines of the conference.
Russia's Foreign Minister Sergei Lavrov responded angrily and accused EU leaders of two-faced Western interference in Ukraine's internal affairs and helping to stoke violent anti-government protests.
Kerry's was the latest statement from Western powers in support of anti-government protests, which have been happening since President Viktor Yanukovich moved away from a pro-EU trade agreement.
Klitschko told reporters at Saturday's security conference that he had the backing of Western diplomats because an unstable Ukraine could bring instability to the whole region.
Another opposition leader, Oleh Tyahnybok, told Al Jazeera: "We are receiving good signals from Europe and the US, but only the declaration of support is not enough.
"Today we think that they should give us a guarantee of a financial and economic support for after the victory. We are asking the world leaders for an active support of Ukrainians," he said.
Stoking the violence
The Russian foreign minister Lavrov accused the West of stoking the violence in Kiev, where top officials and political leaders had backed the protestors during visits.
|US Secretary of State John Kerry meets Ukraine's opposition leaders.
"Why are many prominent EU politicians actually encouraging such actions although back home they are quick to severely punish any violations of the law?" Lavrov said in Munich.
"What does incitement of increasingly violent street protests have to do with promoting democracy?," he said in response to European Council President Herman Van Rompuy, who earlier said Ukraine's future lay in Europe.
Speaking to Al Jazeera from Munich, Leonid Kozhara, the Ukrainian foreign minister, called on Ukrainians to distance themselves from the opposition, saying there was a "big misunderstanding between the government and the opposition".
"For the first time in our country, we can see extremist groups," he said.
He also disputed claims that an opposition activist, Dmytro Bulatov, 35, had been tortured.
"Physically, this man is in good condition, and the only thing he has is a scratch on one of his cheeks."
But Bulatov's lawyer, Ruslan Radetski, told Al Jazeera that he was in intensive care unit after surgery.
"He was kidnapped, beaten up and tortured. The doctors haven't said yet when he will be able to leave the hospital, treatment is under way."
With additional reporting by Tamila Varshalomidze from Kiev