Ukraine, Russia and the European Union have signed a deal that will see Moscow resume vital supplies of gas to Ukraine over the winter.
Russia agreed to resume supplies in return for payments funded in part by Ukraine's Western creditors.
It comes as conflict rumbles on despite a ceasefire with pro-Russian rebels in eastern Ukraine.
After several failed rounds of talks in recent weeks, the accord also eases concerns that a new "gas war" could disrupt winter supplies if energy to EU states notably through pipelines shut down across Ukraine since June.
With overnight temperatures already nudging below freezing in Ukraine, European Commission President Jose Manuel Barroso hailed a deal confirmed in Brussels barely 24 hours before he and the rest of his team make way for a new EU executive.
"There is now no reason for people in Europe to stay cold this winter," he told a news conference after witnessing the signing of documents by the Russian and Ukrainian energy ministers and EU energy commissioner Guenther Oettinger.
Mr Oettinger said he saw in the agreement a "first glimmer" of detente between Moscow and Kiev in a conflict that has plunged East-West relations into a chill not seen since the Cold War.
Worth $4.6bn in total, the package calls for Ukraine to pay $3.1 billion in two tranches by the end of the year to cover debts for previous supplies from Russia's Gazprom.
Kiev will have $1.5bn, some from existing accords with the EU and IMF, to pay for about 4 billion cubicmetres of new gas until March, for which Russia is insisting on cash up front.
