Moscow ? Ukraine rejected Russia’s last-minute offer to delay briefly a crippling increase in natural gas prices late Saturday, opening the possibility that Moscow could turn off the taps as early as today.

With both sides hovering near a compromise for much of the week, it was not clear whether Russia would follow through with its threat to stop the flow of the heating fuel in the depths of winter, or would make good on President Vladimir Putin’s offer earlier in the day to hold off on a price increase until April. Ukraine has reportedly refused to agree to Russia’s demand that it pay “market prices” for natural gas after that date.

In Ukraine, Russia’s demands that it pay the higher rates are widely seen as a response to the Orange Revolution that a little more than a year ago toppled the country’s pro-Russian government and ushered in President Viktor Yushchenko, whose leanings are toward the free-market economics of the West.

“Russia’s firm position that Ukraine should buy gas at European prices is certainly a reaction to the new political course Ukraine is pursuing now,” Socialist Party parliament deputy Mikola Rudkovsky said in a telephone interview from Kiev, the Ukrainian capital.

The dispute could also have a ripple effect through Europe, which depends on Ukrainian pipelines for transit shipment of about 30 percent of its natural gas needs. Russia has insisted that the flow to Europe would not be interrupted even if Ukraine’s supply was cut off.