Russia and Ukraine have failed to resolve a gas pricing dispute at talks and a 0600 GMT deadline for Kiev to pay $1.95 billion in gas debts still stands, a spokesman for Russian natural gas producer Gazprom said on Monday.
Spokesman Sergei Kupriyanov said that Russia would switch to an advance payment system if it did not receive the money, meaning Moscow could cut off gas supplies to Ukraine. Cutting supplies could disrupt the gas flow to the rest of Europe.
U.S. natgas futures were up nearly 1% to $4.80 in Sunday trading.