"Negotiations with Ukraine on Thursday and Friday produced no results. The [country's] debt for gas consumed in 2007 has not been paid in full," Sergei Kupriyanov said.
The Gazprom spokesman also accused Ukraine of unauthorized consumption of around 1.9 billion cubic meters of Russian natural gas, worth some $600 million.
"To ensure its economic interests, Gazprom will cut supplies to consumers in Ukraine by 25% on March 3 at 10:00 a.m .Moscow time [7:00 a.m. GMT]," Kupriyanov said.
Gazprom issued a similar warning on Tuesday.
Ukraine's First Deputy Prime Minister Oleksandr Turchinov said on Wednesday that his country had paid over $1 billion to Gazprom to clear its debts for Russian gas supplies in 2007. Kiev owed Russia a total of $1.5 billion for natural gas supplies in 2007 and 2008.
Ukraine's national oil and gas company Naftogaz said it had transferred the payment to the import monopoly UkrGazEnergo, its joint venture with Swiss RosUkrEnergo, which holds a monopoly on natural gas exports to Ukraine.
Turchinov, currently on a working visit to Minsk, said on Friday that receiving Naftogaz's payment for 2007 gas supplies from intermediaries was Gazprom's concern.
"It is up to Gazprom to make intermediaries pay the money directly to Gazprom," Turchinov said.
The latest reports quoted Kupriyanov as saying that Gazprom would be ready to continue gas talks with Ukraine at any moment.
"We are ready to continue the negotiations at any moment, if Ukraine provides constructive proposals," the Gazprom spokesman said.
