U.S. intelligence agencies investigating the kidnapping of three Americans in Baghdad last week are focusing their probe on three militant Islamic groups closely affiliated with Iran, U.S. government sources said on Thursday. Asaib Ahl al-Haq, Kata'ib Hezbollah and the Badr Organization are Shi'ite militia groups that are part of Iraq's Popular Mobilization Front, a group closely tied to Iran, according to the New York-based Counter Extremism Project advocacy group.