 Israeli tanks were seen firing from southern Israel into Gaza on Friday, ahead of an expected ground invasion following a devastating attack by the militant group Hamas.Israel's military on Friday called for all civilians of Gaza City, more than 1 million people, to relocate south within 24 hours. A movement of people of the United Nations called impossible without devastating humanitarian consequences. Israeli warplanes continued pounding Gaza in retaliation for the weekend attacks by Hamas militants that killed more than 1,300 Israelis, mostly civilians.A ground invasion of the narrow and densely populated Gaza Strip, home to 2.3 million people and under siege by Israel, poses serious risks, with Hamas holding scores of hostages kidnapped in the assault.