Concerns about the flow of Russian natural gas to Europe have been raised once again after agents from Ukraine's state security service raided the offices of state gas company Naftogaz as part of an alleged corruption investigation.
A similar raid was attempted on March 5 at a Naftogaz subsidiary. The incidents have Moscow wondering if Ukraine will be able to pay its multimillion-dollar debt to Russia's Gazprom due later this week.
Masked and heavily armed, agents from the Security Service of Ukraine (SBU) burst into Nafotgaz headquarters on March 4. The SBU, which is loyal to President Viktor Yushchenko, was acting on orders from the Ukrainian leader to investigate alleged corruption.
Yushchenko spokeswoman Iryna Vannykova has defended the raid, saying the use of armed SBU agents was necessary.
"The actions of the SBU are quite tough, as is required by the circumstances of this case. The president is confident that it is necessary to show resolve and firmness in investigating abuses," Vannykova said.
Among the items seized during the raid were documents related to some 11 billion cubic meters of gas that is the former property of RosUkrEnergo, the murky company that until recently served as the intermediary in gas deals between Russia and Ukraine.
RosUkrEnergo lost that role in January, when Ukraine's Prime Minister Yulia Tymoshenko struck a new gas deal with Russia that eliminated the need for an intermediary.
That deal ended a protracted pricing feud between Moscow and Kyiv that cut off gas shipments to more than a dozen European countries during a bitterly cold winter.
But it has since raised questions about the fate of the large gas surplus that RosUkrEnergo was holding at the time.
An SBU spokeswoman, Marina Ostapenko, said the March 4 raid was tied to suspicions that Naftogaz had improperly seized the RosUkrEnergo supplies, which was worth an estimated $900 million.
"[This incident] doesn't need to be blown out of proportion. These are ordinary investigative actions, absolutely ordinary investigative actions in the framework of Ukrainian law," Ostapenko said.
Tymoshenko alleged the SBU raid was an attempt by RosUkrEnergo to seize gas supplies from Naftogaz in order to "paralyze" the country's gas-distribution service. The prime minister, who is locked in a long-term political rivalry with Yushchenko, claims there are links between the president and RosUkrEnergo.
Tymoshenko has appealed to the parliament to suspend the investigation. But SBU agents continued their work on March 5 with an attempted raid at a Naftogaz subsidiary, UkrTransGaz, the company that oversees Ukraine's gas pipelines.
Ukrtransgaz official say SBU investigators later left the building without any documents.
Russian gas giant Gazprom, meanwhile, said in a statement it hopes the events "have no influence on the complete and timely fulfillment" of Naftogaz's payment for February's supplies of Russian gas to Ukraine.
But Naftogaz has sought to assure Gazprom, saying it paid over 80 percent of its bill for February on March 4, and that the remainder will be paid by March 7.
A failure to pay could mean a fresh cutoff of Russian gas supplies to Ukraine, and by extension, to Europe.
The European Union depends on Russian gas transited through Ukraine for the bulk of its energy needs. The January gas war between Moscow and Kyiv left 18 European countries coping with severe gas shortages for nearly two weeks.
RFE/RL's Ukrainian Service director Irena Chalupa contributed to this report