The head of Russia’s Wagner mercenary group, which has been fighting for control of Bakhmut since last summer, announced Friday he would withdraw his forces from the city on May 10 — the day after Russia’s Victory Day military parade — because of insufficient ammunition. In a letter published on his Telegram channel, Yevgeniy Prigozhin demanded that the Defense Ministry sign an order indicating the date on which it would replace Wagner forces involved in a brutal battle for the city in eastern Ukraine.