that russia has moved 90% of its prestage combat power into ukraine. nato warns that the siege of mariupol in the south signals a change in kremlin strategy. russian troops are unleashing more direct attacks after attempts to encircle cities like kyiv have been bogged down. leaders in mariupol say their city is now surrounded. russians are targeting the civilians' most basic needs and the humanitarian crisis grows by the hour. >> we do not have electricity in whole city. we do not have water supply. we do not have sanitary system, and we do not have heating. it continues for one day and a half. so we have continuous shelling for 26 hours, 26 hours they are destroying our city. >> ukraine's military says it will not surrender, the critical port city.