Gazprom spokesman Sergei Kupriyanov said the cutoff would apply only to the Russian gas supplied on the border with Ukraine, which makes up 25% of the total. The other three quarters is pumped from Central Asia.
The spokesman told Ekho Moskvy radio that talks on the debt will be resumed on Tuesday, and that the deadline has been moved from 10:00 a.m. Moscow time (7:00 a.m. GMT) to 6:00 p.m. (3:00 p.m. GMT).
The head of Ukraine's state-owned oil and gas company Naftogaz, Oleh Dubyna, started talks in Moscow earlier on Monday with Gazprom CEO Alexei Miller, in a last-ditch attempt to resolve the debt row. Ukrainian President Viktor Yushchenko is set to arrive in the Russian capital later in the day.
Kupriyanov said: "Progress in the talks has shown that it is hard to expect all problems to be resolved today."
Gazprom and Ukraine agreed in December that a mixture of Russian and cheaper Turkmen gas sold via RosUkrEnergo would cost $179.5 in 2008. The trader said later it would sell Russian gas to Ukraine in January-March for $314 to cover a shortfall in Central Asian supplies.
However, the spokesman said the company could agree on new schemes for deliveries to Ukraine if they are not detrimental to the company.
"As to new proposals, our position is that the situation must not worsen for Gazprom. We are ready to discuss proposals that would not be worse for Gazprom in economic terms, and would ensure secure supplies," Kupriyanov said.
Naftogaz denied on Friday it had any debts to Russia, and the country's Prime Minister Yulia Tymoshenko blamed RosUkrEnergo - the sole supplier of gas to Ukraine which is co-owned by Gazprom and Ukrainian businessmen - for the debt.
She also said she would press for an independent audit of intermediary companies involved in Ukrainian-Russian natural gas deals.
"We will ask for international assistance, for an official group that can check the reliability and stability of the transit of gas to the European Union," Tymoshenko said. "We are asking today for joint monitoring of the financial flows of RosUkrEnergo and UkrGazEnergo beyond Ukraine's borders."
Gazprom's spokesman also said on Monday it had ordered an audit of Russian natural gas supplies to Europe via Ukraine.
"We have invited independent organizations to monitor the volume of gas that enters Ukraine and leaves its gas transit system," Kupriyanov said.
President Yushchenko could discuss the issue at a meeting with his Russian counterpart Vladimir Putin during his visit, said Raisa Bogatyreva, secretary of Ukraine's National Security and Defense Council.
"I am sure market relations in the gas sphere will be discussed," the spokesperson said.
However, Gazprom spokesman said that there is no meeting planned between Yushchenko and the company's CEO Alexei Miller.
