Ukraine's Prime Minister Yulia Tymoshenko has accused Russian oil companies of trying to "bully" her country by causing fuel shortages.
Yulia Tymoshenko has pledged to restore supplies in two weeks
Petrol stations began running out of fuel, 80% of which comes from Russian sources, after Ukraine froze prices.
Ms Tymoshenko said Russian firms, including Lukoil, Tatneft and TNK-BP, had suspended deliveries and created an "artificial crisis".
However, the oil companies said repair works had restricted supplies.
Russian media quoted representatives of the firms as saying that oil was still being pumped to Ukraine.
TNK-BP, which is jointly owned by UK oil giant BP, said it was supplying a smaller volume of crude because of work on one of its pipelines.
Problems began last month, when the Ukrainian government froze petrol prices after accusing Russian firms of conspiring to increase them.
Adding to the pressure, Moscow announced an increase in crude oil export duties from $102 to $136 a tonne, to take effect from 1 June.
With two of Ukraine's six refineries closed for repairs and maintenance by their Russian owners, petrol shortages have ensued.
By last weekend, petrol stations throughout Ukraine - run mainly by Russian companies - were selling fuel only to drivers who had special coupons or customer cards, turning numerous cars away.
Ms Tymoshenko said Russian companies had failed to supply 20,000 tonnes of crude oil to a third refinery, Kremenchuk, between 7 and 12 May.
"Oil deliveries to Ukraine are being deliberately stopped, even though all contracts have been paid for," she said.
"It is no more than a plot, sabotage. They want to put Ukraine in its place."
Ms Tymoshenko said Russia could not come to terms with the fact that a new President, Viktor Yushchenko, and a new government had come to power in Ukraine.
She said Ukraine was negotiating contracts to buy oil from Kazakhstan instead and petrol supplies would be back to normal by June.
Relations between Kiev and Moscow have been strained since last year's Ukrainian "orange revolution" that resulted in victory for the pro-Western opposition led by Mr Yushchenko.
Russia had backed rival candidate Viktor Yanukovych.
The Russian authorities accuse Ms Tymoshenko, a former gas industry oligarch, of bribery and are pursuing a criminal case against her.
On Monday, Ms Tymoshenko cast doubt on Ukraine's record growth figures for 2004, produced under the administration of former President Leonid Kuchma.
She said the government would "seriously analyse" the statistics for GDP and industrial output, adding: "From our point of view, we may put a question mark here."
According to the figures, GDP grew by 12.1% last year.