Nine U.S. citizens have been killed in the fighting between Hamas and Israel, a State Department spokesman said Monday, the third day of fighting since Hamas’s attack on Israel began. Israel announced a full siege of the Gaza Strip, with Defense Minister Yoav Gallant saying there would be “no electricity, no food, no fuel.” The Israeli government has declared war on the Palestinian militant group, and U.S. officials expect Israel to launch a ground incursion into densely populated Gaza early this week, according to people familiar with the matter. Earlier Monday, Hamas said it struck the Israeli cities of Jerusalem, Tel Aviv, Sderot, Ashkelon and Ashdod with rockets; later in the day, the Israel Defense Forces said they intercepted militants crossing into Israel from Lebanon.