An airstrike killed a senior Islamic State leader believed to be the head of the group in Iraq and Syria on Friday, in a joint Iraqi and U.S. operation using intelligence from both countries, Iraq's prime minister said. The Islamic State leader, Abdallah Makki Muslih al-Rufay'i, who was also known as Abu Khadija, was 'one of the most dangerous terrorists in the world,' the Iraqi prime minister said in a statement.