Russia has stopped all gas supplies to Ukraine after negotiations to end a dispute over unpaid bills and prices collapsed.
Russia's gas giant Gazprom said it turned off the taps this morning when its contract to supply Ukraine ended.
There have been fears that the row could lead to energy shortages in Europe, as pipes across Ukraine carry about a fifth of the EU's gas needs.
The US has urged the restoration of normal gas deliveries to Ukraine.
White House spokesman Gordon Johndroe said: 'We hope that Russia and Ukraine can resolve their dispute over the gas debt and the terms of their natural gas supply arrangements in a transparent, commercial manner.
'We urge both sides to keep in mind the humanitarian implications of any interruption of gas supply in the winter.'
