US intelligence agencies investigating the kidnapping of three Americans in Baghdad, Iraq last week are focusing their probe on three militant Islamic groups closely affiliated with Iran, US government sources said on Thursday.Asaib Ahl al-Haq, Kata'ib Hezbollah and the Badr Organization are the principle focus of the investigation into the armed kidnapping of the three Americans in the Dora neighborhood, south of Baghdad, the sources said.The three men are employed by a still-unidentified small company doing work for General Dynamics under a larger contract with the US Army.The US government still does not know if any of the three groups kidnapped the three men. While the three groups have close ties to Iran, sources said the United States does not believe Iran was involved in the kidnapping, or that the three are being held in Iran.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 Counter Terrorism Project, a New York-based advocacy group.