Kupriyanov said Ukraine had sent a letter saying it is taking 60 million cubic metres a day of Russian gas from transit pipelines.
"This is the volume that European consumers won't get," Kupriyanov said.
The amount would have effectively reduced exports to Europe by 17 per cent.
The European Union said on Wednesday that Ukraine had not told it about any moves on transit gas.
Dmitry Medvedev, the Russian president elect, had threatened further cuts in gas to Ukraine unless a the $600m debt was settled and a 2008 contract signed.
Viktor Yushchenko, the Ukrainian president, insisted on Wednesday that Ukraine would not disrupt gas supplies to Europe because it would use stored gas to make up its commitments.
Before the Gazprom statement, Yulia Tymoshenko, the Ukrainian prime minister and Yushchenko's political rival, also said that Ukraine would uphold its commitments to Europe.
"Ukraine is a reliable partner. We will not stray one iota from our obligations in terms of exporting natural gas to European countries," she said.
The development mirrors a pricing dispute between Ukraine and Gazprom in 2006, when Russian gas supplies to Europe were briefly disrupted in the middle of the winter.
The row raised fears among European nations and prompted the EU to question the reliability of Gazprom as the supplier of a quarter of Europe's gas.
The EU and the US had called on the two sides to find a peaceful solution to the latest dispute.
On Tuesday, Tom Casey, the deputy spokesperson for the state department, said: "This dispute underscores the need for greater transparency in the Russia-Ukraine gas trade and also highlights again ... that there needs to be a predictable flow of energy for Ukraine and the rest of the European market."