Russia's state gas monopoly accused Ukraine of blocking transit of Russian gas to Europe hours after supplies were restarted, extending the bitter energy crisis that left large parts of Europe cold and dark.
Gazprom began pumping gas into Ukraine shortly after 10 a.m. Moscow time (0700 GMT), but four hours later Gazprom's Deputy Chairman Alexander Medvedev said Ukraine's pipeline system had failed to carry it on to Europe.
"Ukraine didn't open any export pipelines," Medvedev said in a call-in with reporters. "They just shut down the entry of the pipeline in the direction of the Balkans. We don't have the physical opportunity to pump the gas to European customers."
Ukraine's state gas company Naftogaz declined comment.
Russia has accused Ukraine of stealing gas intended for Europe and only restarted supplies after a EU-led monitoring mission was deployed to gas metering and compressor stations across Ukrainian territory. The observer mission includes EU, Russian and Ukrainian officials and representatives of European energy companies.
EU spokesman Ferran Tarradellas Espuny said "very limited" amounts of gas started flowing to Ukraine and only through one entry point from Russia to Ukraine.
He said EU monitors still do not have full and free access to dispatching centers in Kiev or Moscow to check the gas flow.
"The information that we have from our monitors in Russia is that little or no gas is currently flowing and we are not at this stage jumping to conclusions as to why this is the case," said another EU spokeswoman, Pia Ahrenkilde Hansen. "This situation is obviously very serious and needs to improve rapidly."
Medvedev accused Ukraine of barring observers from a central control room for its pipeline network and underground gas storage in violation of an EU-brokered monitoring deal.
Ukraine has fiercely denied the siphoning accusation, but Prime Minister Yulia Tymoshenko warned on Monday that Ukraine will have to use some gas from Russia as so-called "technical gas" to power compressors that push Europe-bound gas through its 23,000 miles of pipelines.
Gazprom has insisted it is Ukraine's duty to provide the gas. Gazprom spokesman Sergei Kupriyanov warned Tuesday that "the amount of Russian gas pumped into Ukraine's pipeline network must strictly correspond to the amount of gas flowing out of Ukraine."
Valentyn Zemlyansky, the spokesman for Ukraine's Naftogaz, said Ukraine will continue to use some of the Europe-bound gas as fuel for its pumping stations and denounced Gazprom's demands as an "attempt to put pressure on Ukraine."
"Where else will we take those volumes (of gas) from?" Zemlyansky said.
Russia's President Dmitry Medvedev already has ordered Gazprom to reduce supplies if it again sees Ukraine siphoning gas, and suspend it completely if it believes Ukraine continuously steals gas.
Russia supplies about one-quarter of the EU's natural gas, 80 percent of it shipped through Ukraine, and the disruption came as the continent was gripped by freezing temperatures in which at least 11 people have frozen to death.
The gas cutoff has affected more than 15 countries, with Bosnia, Bulgaria, the Czech Republic, Hungary, Serbia and Slovakia among the worst hit. Sales of electric heaters have soared and thousands of businesses in eastern Europe have been forced to cut production or even shut down.
Russia stopped gas supplies to Ukraine on Jan. 1 amid a contract dispute, but continued sending gas to Europe across the Ukrainian territory until Jan. 7 when it fully halted shipments over alleged Ukrainian theft.
Russia used the gas dispute to reaffirm its push for prospective gas pipelines under the Baltic and the Black Sea which would bypass Ukraine. But EU officials said the crisis should encourage a search for independent energy sources and supply routes, such as the U.S.-backed Nabucco pipeline that would carry Caspian energy resources circumventing Russia.
While the current gas crisis was triggered by a pricing dispute, relations between the two ex-Soviet neighbors have been strained since the 2004 Orange Revolution in Ukraine led to the election of a pro-Western government in Kiev.
Ukraine's efforts to join NATO and its support for the former Soviet republic of Georgia in its war with Russia in August has angered the Kremlin. Last week, U.S. officials had warned Russia not to use its energy resources as a weapon against Europe.
Russia still will not send natural gas to Ukraine for domestic consumption. The neighbors remained deadlocked over the price Ukraine should pay for gas in 2009 and the amount Russia should pay for transporting gas through Ukraine.
Ukraine in 2008 paid $179.50 per 1,000 cubic meters of Russian gas and turned down Gazprom's proposal of $250 for 2009 — a substantial hike for the economically distressed country but still far below some $450 that European customers pay.
The latest round of price talks ended Sunday without result.