President Vladimir Putin agreed on Tuesday to lead Russia's biggest political party, a move that will bolster his power after he steps down as Kremlin leader next month, Reuters reported. "I accept the invitation of the party. I am ready to take on myself the additional responsibility and head the party," Putin told cheering delegates at a United Russia congress in Moscow. Putin has already said he will serve as prime minister once his protege, Dmitry Medvedev, is sworn in as president on May 7.