Russia cut shipments to the cash-strapped republics earlier this year, but turned the gas back off after reaching agreements on repayment terms.
But the "situation is not only not getting better but worsening" despite regular talks, Gazprom's chief engineer, Vladimir Podmarkov, told Itar-Tass.
Ukraine, the largest debtor, now owes about 2 trillion rubles ($1 billion), more than twice what it owed at the beginning of 1994, and has paid Gazprom little since the end of the first quarter.
One reason Russia continues shipping gas is that its pipeline to European customers passes through Ukraine. Gazprom says about 575 million cubic meters of Russian gas go through the pipeline every day. About half stays in Ukraine, the rest is for other customers.
Russia warned Ukraine that it might shut off the gas if the debt issue is not resolved by Sept. 1, Interfax said.
Belarus currently receives 26 million cubic meters a day of Russian gas, and owes 700 billion rubles ($325 million) for previous shipments, according to Gazprom.
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