Russia's state-owned energy giant Gazprom will cancel a gas price discount for Ukraine after the revolution-gripped country said it would not be able to pay in full for its February supply.
But the Russian government said it may offer a loan to Ukraine of between $2bn (£1.2bn, €1.45bn) and $3bn so it can pay off its debt with Gazprom, on who it relies for a significant portion of its energy supply.
"Those who don't pay for goods supplied must understand they will face consequences and may lose shipments on easy terms," said Dmitry Medvedev, Russia's prime minister, according to Russia's Interfax news agency.
Ukraine is at the centre of a global political battle after a revolution ousted the country's Russia-allied president, Viktor Yanukovich.
Russian troops are on the ground in Ukraine's Crimea region, where Russia has many interests.
Vladimir Putin, Russia's president, insists this is to keep the peace amid the throes of revolution.
But the European Union (EU) and the US have said Russia's entry into Crimea is an act of aggression that breaches national sovereignty.
There is a tussle for influence over Ukraine between the west and Russia.
Russia seeks to defend its financial interest in Crimea, where it owns much of the industry and around 60% of the population is ethnically Russian.
However, many Ukrainians want to move closer to the EU and away from Russia, one of the reasons there was unrest and eventually a revolution.
Ukraine's parliament has just ratified a €610m loan from the EU, but it will need much more financial help if it is to plug a $70bn black hole in public finances identified by the new prime minister, Arseny Yatseniuk.