An increasingly bloody onslaught in the Ukrainian city of Mariupol has descended into street-by-street guerrilla warfare, as Moscow vies to claim its first strategic victory of the war. Amid bombings on civilian buildings and claims of forced deportations, Russian officials on Sunday called for Ukrainian troops to lay down arms and flee the city during a two-hour window Monday morning or face further assaults and a “military tribunal.” Ukraine’s deputy prime minister rejected the calls to surrender.