As a dispute between Russia and Ukraine over gas deliveries for Europe worsens, seven eastern European and Balkans countries have reported a complete halt to their supplies from Russia.
The European Union, most of whose member states are in the grip of severe winter weather, has called the shutdown completely unacceptable.
Russia and Ukraine are blaming each other for the dispute
A day earlier, Turkey reported that all its gas supplies via Ukraine have been cut. Romania reported a 75% reduction. Bulgaria, Greece and Macedonia also report shortfalls.
Slovakia says it will declare a state of emergency over the drop in gas supplies.
Bulgaria says it has sufficient supplies for only a few days. It says no more gas is flowing through a pipeline that also supplies Turkey, Macedonia and Greece.
The giant Russian energy company Gazprom says Ukraine has shut three of the four pipelines for Russian gas to Europe.
Gazprom says only 40 million cubic metres of gas is getting through to Europe, instead of 225 million cubic metres.
The European Commission says the cut is "completely unacceptable". The EU depends on Russia for about a quarter of its total gas supplies, 80% of which is pumped through Ukraine.
Ukraine's main energy company, Naftogaz, says talks with Gazprom aimed at resolving the crisis are due to resume in Moscow on Thursday.
The BBC reports Russia stopped supplying gas to Ukraine on New Year's Day in a dispute about unpaid bills. The row comes amid a cold snap across Europe.
Gazprom says Ukraine owes it more than $US600 million; Ukraine says it has paid the debt.
A similar dispute at the beginning of 2006 led to gas shortages in several EU countries.
Gazprom wants Ukraine to pay $US450 per 1,000 cubic metres of gas - more than double what Kiev says it is willing to pay, but less than what most EU states pay.