The world may be witnessing "the last genuine opportunity the people of Ukraine have to establish a democratic republic in a way that is economically prosperous and fully integrated within Europe," Vice President Joe Biden opined on Monday.

"But it is being challenged," he warned a group of international business leaders gathered at the U.S. Chamber of Commerce for the first-ever U.S.-Ukraine Business Forum.

Biden said Ukraine is now "under siege" from Russian military incursions into eastern Ukraine. That includes Moscow's moving heavy-equipment over the disputed border, lobbing missiles into the area, and sending "Russian-hired thugs and mercenaries" into the former Soviet republic, Biden said.

Beyond potentially denying Ukrainians the right to choose their own path, the freedom and peace of Europe is at stake if Putin succeeds in destroying the experiment in democracy and openness underway in Ukraine since the Orange Revolution, Biden said.

"Russia is not just intervening militarily," he said, "Russia is trying to squeeze Ukraine financially," and is using economic pressure and access to energy as political weapons. "It is attempting to export corruption and oligarchy" to it's former satellite he said, calling those undemocratic practices the new foreign policy tools of Russian President Vladimir Putin.

Putin is trying to undermine Ukraine any way he can, including causing it to economically collapse, which is "his first preference," Biden said.

"This is it Mr. Prime Minister; this is it," Biden said to Ukrainian Prime Minister Arseniy Yatsenyuk, with whom he shared the stage.

The summit, co-hosted by the U.S. Chamber of Commerce and the Commerce Department, is intended to encourage U.S. businesses to operate in or otherwise do business with Ukraine. It's part of Commerce Secretary Penny Pritzker's "commercial diplomacy" effort.

"Her message to leaders in the country was clear: sustainable economic growth is the gateway to long-term political stability for the people of Ukraine, and the United States is here to help," a Commerce Department statement read last September after Pritzker returned from diplomatic trip to Ukraine.