World leaders, including Prime Minister John Howard, are hailing the killing of terrorist leader Abu Musab al-Zarqawi as a significant breakthrough for Iraq. Iraqi Prime Minister Nuri al-Maliki has announced that Zarqawi "has been eliminated" in an airstrike on a safe house in Baquba, 60 kilometres north of Baghdad. "What happened ... is the result of collaboration from people who facilitated the operation conducted by Iraqi police and multinational forces," Mr Maliki said. "This is a message to those who choose the path of violence to change their direction before it is too late. "I thank our forces, our police...