Tensions between the United States and Iran are running high after Iran shot down an unarmed U.S. Navy drone. American officials say the drone was in international airspace today, but Iran claims the drone was in Iranian airspace on a spying mission. U.S. Defense officials have said this was an unprovoked attack. This is the second time in a week Iran has targeted a U.S. drone. It tried to shoot one down as it was surveilling last week's attack on one of two tankers in the Gulf of Oman. The U.S. blames Iran for attacking the tankers, which Iran denies.