Russian Prime Minister Vladimir Putin arrived Tuesday in Kiev to meet with pro-Kremlin Ukrainian President Viktor Yanukovych to discuss the possibility of Ukraine joining a regional economic bloc.
The visit coincided with a move by prosecutors in Kiev to investigate Tymoshenko for a gas deal she helped broker while serving as prime minister in 2009.
Russian gas monopoly Gazprom in January 2009 cut of the gas to Ukraine because of disputes over contracts and debts. A new gas deal put tight pressure on Ukraine, though Yanukovych was able to broker a better deal in exchange for an extended lease for the Russian Black Sea fleet in Crimea.
Renat Kuzmin, the deputy prosecutor general in Kiev, was quoted by the Financial Times as saying a case was launched against Tymoshenko for "abuse of power linked to the signing of gas contracts in 2009."
Tymoshenko lost a bitter election contest to Yanukovych in 2010 and has since faced charges she misused federal money meant for environmental projects to pay for pension funds during her tenure as prime minister.
The opposition leader in statements posted on her Web site said she viewed the latest charges as a diversion from the president's continued courtship with the Kremlin.
"This is theater of the political absurd," she said.
Ukraine hosts 80 percent of all the Russian gas bound for European markets.
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend
Pot vending machine to debut