Israel has been shelling Gaza for a fifth day. Media buildings in Gaza City and a number of other targets have been hit by Israeli shells. Thousands of Israeli troops backed by tanks have also been massing along the border in preparation for a possible ground operation. Palestinian officials say more than 60 people have been killed since the Israeli air offensive began with the killing of Hamas's military chief, Ahmed Jabari, in an airstrike on November 14. Rockets fired from Gaza have killed three Israeli civilians.