Israel’s military says it has withdrawn its forces from the southern Gaza city of Khan Younis, wrapping up a key phase in its ground offensive against the Hamas militant group. But defense officials say troops are merely regrouping as the army prepares to move into Hamas’ last stronghold, Rafah. Rafah shelters some 1.4 million people, and the prospect of an offensive has raised global alarm. The withdrawal brings Israel’s troop presence in the territory to one of the lowest levels since the war began. It is a milestone as Israel and Hamas mark six months of fighting.