KYIV, April 21 (Reuters) - President Vladimir Putin claimed victory in the biggest battle of the Ukraine war on Thursday, declaring the port of Mariupol "liberated" after nearly two months of siege, despite hundreds of defenders still holding out inside a giant steel works. In a televised meeting with his defence minister inside the Kremlin, Putin said there was no need for a final confrontation with the last defenders who were boxed in after surviving nearly two months of Russia's siege. "I consider the proposed storming of the industrial zone unnecessary," he told Defence Minister Sergei Shoigu in a televised...