Alexander Medvedev, Gazprom's deputy chairman, said that if the EU leadership thoroughly investigated the causes of the dispute, Ukraine's bid to join the EU would be in question.
"A transit blackmailer, who blackmails both Russia and Europe at the same time, is not the best possible candidate for EU membership," he said, referring to Ukraine. "Such an investigation would also demonstrate Gazprom's complete reliability as a gas supplier."
Medvedev described the EU-Ukraine agreement on investment in the Ukrainian gas transport system as "an irresponsible and unfriendly move on the part of the EU."
He added that over the past three years Gazprom had invested more than $30 billion in Ukraine's gas network, but was cut out of the deal.
"Unfortunately, our Ukrainian partner preferred to use its monopoly position as transit country for Russian gas to Europe for blackmail," he said.
Kiev and Brussels signed an agreement to modernize Ukraine's Soviet-era gas pipeline network last week, triggering an angry reaction from Russia, which exports most of its Europe-bound gas via Ukraine.
Moscow said earlier it had been deliberately excluded from the deal. It delayed inter-government talks with Kiev and threatened to review energy ties with the European Union if its interests continued to be disregarded.
However, Ukraine's president said on Monday that his country's natural gas cooperation agreement with the EU would not lead to a new "gas war" with Russia.
Viktor Yushchenko said that the agreement with the EU was designed to make exports more reliable and transparent.
Ukrainian Premier Yulia Tymoshenko has said on several occasions that Russia will have a full role in the modernization of Ukraine's gas network.
