By Pavel Polityuk KYIV (Reuters) -Russian President Vladimir Putin claimed victory on Thursday in the biggest battle of the Ukraine war, declaring the port city of Mariupol “liberated,” although hundreds of Ukrainian troops and civilians were still holding out inside a giant steel works. The United States disputed Putin’s claim and said it believed Ukrainian forces still held ground in the city. Putin ordered his troops to blockade the steel complex, where Ukrainians were told earlier to either surrender or die. Ukraine said Putin wanted to avoid a final clash with its forces in Mariupol, as h…