A crackdown on nationwide protests in Iran has killed at least 538 people and even more are feared dead, activists said Sunday, while Tehran warned that the U.S. military and Israel would be "legitimate targets" if America uses force to protect demonstrators. Another over 10,600 people have been detained over the two weeks of protests, said the U.S.-based Human Rights Activists News Agency, which has been accurate in previous unrest in recent years. It relies on supporters in Iran crosschecking information. It said 490 of the dead were protesters and 48 were with security forces. With the internet down in Iran and phone lines cut off, gauging the demonstrations from abroad has grown more difficult. The Associated Press has been unable to independently assess the toll. Iran's government ha