Ukraine has rejected Russia’s demand to surrender the besieged city of Mariupol in exchange for humanitarian corridors, saying the Kremlin was holding its citizens hostage.

Russia’s Ministry of Defense on Sunday had issued Ukraine a 5 a.m. deadline to surrender the strategic southern port city in exchange for the opening of eastern and western humanitarian corridors, according to state-run RIA Novosti.

Ukrainian soldiers in Mariupol were an “historic choice” to either lay down their arms or side with “bandits” and be subjected to a “military tribunal” greater than that they have already experienced, the military said.