Russia cut gas shipments to Ukraine on January 1, after a dispute over prices stalled the renewal of a gas agreement between the countries.
Russia then halted all gas shipments to Europe via Ukraine on January 7, alleging that Ukraine was siphoning off Europe-bound gas. Many European countries were subsequently left without heating in freezing cold weather.
In Moscow on Monday, Yulia Tymoshenko, the Ukrainian prime minister, and Vladimir Putin, her Russian counterpart, agreed a deal ending the price dispute.
Tymoshenko said Kiev would pay less than $250 per 1,000 cubic metres of Russian gas in 2009.
The office of Ukraine's president criticised the deal, saying it handed victory to Moscow and would damage the Ukrainian economy.
Bohdan Sokolovsky, energy adviser to Viktor Yushchenko, the Ukraininan president, said that by agreeing to pay higher rates for Russian gas this year without increasing the amount it charges Russia for gas transit to Europe, Ukraine would be "subsidising" Gazprom.
Separately, the deputy leader of Ukraine's leading opposition party, the Regions Party, told Interfax that the deal was a defeat for the Ukrainian government because it would raise gas prices to more than $300 per 1,000 cubic metres.
The European Commission has remained cautious over the Ukraine-Russia deal, demanding to know precisely when gas taps will be turned back on, and said monitors would assess the supplies.
Naftogaz, the Ukrainian state energy company, has warned it could take up to a day and a half to pump gas to Ukraine's western border once Russia resumes shipments.