Tymoshenko is serving a seven-year prison term after a conviction on charges she abused her authority when helping broker a 2009 natural gas contract with Russian energy company Gazprom. The deal broke a contractual impasse that left downstream European consumers in the cold for weeks, though Ukrainian officials maintain the deal bruised an economy battered by recession.
Putin said his position was that Tymoshenko was convicted for signing a gas contract with his country.
"Prior to the signing of the contracts, our lawyers thoroughly analyzed Russian, international and Ukrainian laws," he was quoted by Russia's state-run news agency RIA Novosti as saying. "We never sign contracts contradicting the laws of the contract partner country, in this case Ukraine."
Tymoshenko's supporters say the charges are politically motivated. She led the country's Orange Revolution but lost a presidential election to Viktor Yanukovych in 2010.