Russian Prime Minister Vladimir Putin is visiting Ukraine today, with Russian gas supplies to Ukraine back on the agenda of his talks with Ukraine's Moscow-friendly leadership.
About 80 percent of Russian gas exports to the European Union transit Ukraine, and Russia has long said it wants a stake in Ukraine's pipeline system.
Ukraine, which also depends heavily for its own consumption on Russian gas imports, wants Russia to cut prices.
During his last visit in April, Putin proposed a merger between Russia's energy giant Gazprom and Ukraine's state-owned Naftogaz.
Ukraine has ruled out a merger, but Ukrainian officials have said a joint venture between the two countries is a possibility if it buys cheaper gas.
Putin was expected to discuss cooperation in gas and nuclear energy, aviation, space and agriculture when he met with Prime Minister Mykola Azarov and President Viktor Yanukovych, whose election in February ushered in improved relations with Moscow.
compiled from agency reports