The same thing happened again Wednesday, said Oleh Dubina, the head of Naftogaz.

"Unfortunately, we answered the same way: we cannot leave our regions without gas," Dubina said.

Putin said it was up to Ukraine to make the deliveries possible.

"We opened the tap, and are ready to supply gas, but on the other side, the tap is closed," Putin told the visiting prime ministers. "Nobody, no transit country, has the right to abuse its transit location to take other customers hostage."

Bulgaria has lost all its gas supplies, and Slovakia nearly all.

"Ukraine is losing the trust of European partners because of its behavior," Slovakian Prime Minister Robert Fico said.

Medvedev said Gazprom should sue Ukraine over what Gazprom chief Alexei Miller told him was $1.1 billion in lost income. Russia and Gazprom "cannot lose so much money in the current conditions," Medvedev told Miller in televised comments, referring to the global financial crisis.

Gazprom cut off all gas supplies meant for Ukrainian consumption on Jan. 1, amid a price dispute. It stopped sending any gas at all into Ukraine's pipeline system on Jan. 7, alleging that Ukraine was siphoning off supplies destined for Europe.

Ukraine has denied the charges, claiming that Russia has not sent enough so-called "technical gas" to pump the rest of the gas west to Europe. Who pays for the technical gas is also in dispute — and the amount used by Ukraine's sprawling, inefficient system runs into millions of dollars each day.

The clash has affected millions of people, mostly in eastern Europe, in the midst of winter. Thousands of businesses have had to shut down or cut production, forcing workers into involuntary layoffs.

Serbia reported Wednesday that its power grid was getting overloaded as thousands switched to electric heat and urged residents to conserve energy. It also said air pollution in Belgrade, the capital, was increasing amid the shift from natural gas to oil.

Hungary issued its first-ever smog alert in Budapest last week for the same reason, while Hungarian gas importer Emfesz said it has already sued Ukraine in EU courts and Naftogaz in Hungarian courts.

Ukrainian Prime Minister Yulia Tymoshenko, who met with Fico and Stanishev in Kiev, said Ukraine would resume supplies of Russian gas to Europe if Russia agrees to provide 21 million cubic meters of "technical gas."

But Dubina sounded more conciliatory, asking Moscow to lend Ukraine that gas and promising to later pay it back.

Russia and Ukraine are deeply at odds over what Ukraine will pay for Russian gas in 2009. Ukraine last year paid $179.50 per 1,000 cubic meters; Russia wants Ukraine to pay market price for gas, about $450.