By Pavel Polityuk KYIV (Reuters) – Russian President Vladimir Putin claimed victory in the biggest battle of the war in Ukraine on Thursday, declaring the port city of Mariupol “liberated” after nearly two months of siege. However, hundreds of fighters and civilians in dozens of bunkers were still holed up inside a huge steel works. Putin ordered his troops to blockade the complex “so that not even a fly” could escape. Ukraine said Putin wanted to avoid a final clash with its forces in the city as he lacked the troops to defeat them. In Washington, U.S. President Joe Biden authorized a further…