Ukrainian Prime Minister Arseniy Yatsenyuk said ousted President Viktor Yanukovych left the economy in ruins. A Yanukovych decision in November to suspend efforts to move closer to the European Union sparked national protests that lasted through February.
Russia has since annexed the Crimean peninsula, raising concerns about the Kremlin's influence in the region. European consumers get about a quarter of their gas needs met by Russia, though the bulk of that flows through the Soviet-era transit network in Ukraine.
The House and Senate this week passed a $1 billion aid package for Ukraine.
U.S. Sen. John Hoeven, a North Dakota Republican who visited Ukraine last week, said Russia's energy power should serve as a lesson for North America. Recent events in Ukraine, he said, "illustrate the importance of developing our own domestic energy resources to achieve energy security, which is central to economic and national security."
North Dakota is the second-largest oil producing state in the country.
Some U.S. lawmakers have pressed for more oil and natural gas exports to Europe to counter Russia's influence.