MOSCOW — President Vladimir V. Putin and other senior Russian officials threatened on Wednesday to restrict supplies of natural gas to Ukraine, and they reiterated the Kremlin’s contention that Ukraine owes Russia more than $16 billion in unpaid gas bills and other debts.

The declarations, at a government meeting just outside Moscow, were the latest pointed reminders to the West that Russia holds substantial sway over Ukraine’s financial future — even without a military incursion into eastern Ukraine. The declarations also seemed intended to increase the Kremlin’s leverage in talks with the United States over resolving the political crisis.

“If this critical situation really continues like this, I believe there is every reason to apply the transition to a prepayment system for gas supply,” Prime Minister Dmitri A. Medvedev said, according to a Kremlin transcript of the meeting. Mr. Putin said he agreed, but urged Mr. Medvedev and other officials, as well as Gazprom, the state-controlled energy company, to delay such a move “given the difficult situation in Ukraine.”

Russia has made clear that it will use every bit of leverage it can muster to prevent Ukraine from drifting further into the West’s sphere of influence.