Russian President Vladimir Putin told his government to develop plans to replace imports from Ukraine and said Russia can't subsidize its neighbor permanently, increasing economic pressure as the government in Kiev battles separatists.

Russia "continues to provide economic support and subsidize Ukraine's economy with hundreds of millions and billions of dollars," Putin told a cabinet meeting outside Moscow yesterday. "This situation, of course, can't go on forever."

Putin urged talks before possibly requiring Ukraine to make advance payments for natural gas, and Prime Minister Dmitry Medvedev said the country owes Russia $16.6 billion in energy debts. Ukraine's government, which is trying to accelerate approval for an international bailout, said yesterday it may use force to remove pro-Russian activists from official buildings in the east.

Ukraine's pro-European cabinet accuses Russia of stoking unrest in the regions near the nations' border in a bid to destabilize next month's presidential election.

That assessment was echoed by U.S. Assistant Secretary of State Victoria Nuland, who said the "evidence is overwhelming" that Russian intelligence agencies planned and executed the takeovers of government buildings in eastern Ukraine.

"I don't think that we have any doubt that the preponderance of evidence indicates direct Russian involvement," she told the U.S. Helsinki Commission yesterday.

The Ukrainian government also says Russian bans on goods such as dairy products are politically motivated. The U.S. is providing legal advisers to help Ukraine file a complaint against Russia with the World Trade Organization, Nuland said in Washington.

The U.S. also is working with Ukraine and the European Union in an effort to limit Russia's ability to use the threat of a natural-gas cutoff, Nuland said.

"The most likely source of quick gas for Ukraine in the event of a shutoff comes in reverse flows from Slovakia, from Hungary, from Poland," she said. "This requires some upgrading of infrastructure, it requires some investment, it requires some political decisions."

Finance chiefs from the Group of Seven countries will discuss the crisis in Ukraine at talks in Washington today, a G-7 official said. Along with financial aid for Ukraine, the U.S. and its economic allies have been weighing tougher sanctions on Russian companies and industries if Putin's government moves militarily against Ukraine.

The deterrent impact of the sanctions threat depends on whether Putin believes the Europeans will take such actions, said former U.S. diplomat Nicholas Burns, who was under secretary of state for political affairs from 2005 to 2008.

"If the Europeans would threaten with as loud a voice what the White House is saying, that could knock Putin back a little bit," Burns, now a professor at the John F. Kennedy School of Government at Harvard University in Cambridge, Massachusetts, said in a phone interview.

"It could cause him to reconsider what he's doing because he needs integration, he needs capital investment, he needs trade to fuel the Russian economy. But you're not seeing that united Western response."

Russia takes VOA off air