Gaza City -- - Gaza gunmen killed 18 alleged spies for Israel on Friday, including seven who were lined up behind a mosque with bags over their heads and shot in front of hundreds of people. In new violence, a 4-year-old Israeli boy was killed by Palestinian rocket fire, while four Palestinians were killed in Israeli air strikes in Gaza. The killings came a day after an Israeli air strike on a house in southern Gaza killed three senior military leaders of Hamas. The three had played a key role in expanding Hamas' military capabilities, including building a network of attack tunnels into Israel and smuggling weapons.