Russia has further reduced the amount of gas it is supplying to Belarus because of a dispute over payments - now amounting to a 60% cut.
Russia's gas monopoly Gazprom said it cut supply by 15% on Monday, 15% on Tuesday, and another 30% on Wednesday.
Gazprom said there had been no effect on deliveries elsewhere.
The company is demanding Belarus pay almost $200m (?135m) it says is owed for Russian gas but Belarus says Russia owes money for using pipelines.
"The Belarusian side is undertaking no action to settle the debt for Russian gas supplies," Gazprom's chief executive Alexei Miller said in a televised appearance on Wednesday.
Gazprom has threatened to continue tightening the taps until supply is down to only 15% of its previous level.
Belarus said on Tuesday it would suspend Russian transit gas deliveries via Belarus to other European countries.
President Alexander Lukashenko warned of a "gas war", and insisted that Belarus is owed $260m (?176m) by Russia in fees for using transit pipelines.
Most Russian gas bound for European countries goes via Ukraine, but Lithuania, Germany and Poland rely on supplies through Belarus. Even so, gas supplies for those three countries could be re-routed via Ukraine if necessary, Gazprom says.
Russia increased the price of gas supplied to Belarus from $150 per 1,000 cubic metres of gas last year, to $169.20 in the first quarter of 2010 and $184.80 in the second.
But Belarus has continued to pay $150. Gazprom said at that rate it could owe $500m or $600m by the end of the year.
Gazprom said in a statement on Wednesday that Belarus had paid for May's deliveries at a higher price, thus "recognising the need" to pay increased rates - but that it still had to settle debts accrued in the first four months of the year.
Belarus has previously insisted Russia provide it with cheap oil and gas as part of a customs union deal that is due to come into force next month.
Russia and Belarus are supposed to be close allies but have had several rows in recent years, particularly over energy supplies.