Newly declassified documents are shining a new light on the extent to which Iran trained and armed Iraqi militias that attacked U.S. troops during the Iraq War, according to files reviewed by The Wall Street Journal. The report comes from the interrogation of Qais al-Khazali, the leader of a major Shiite militia group that has recently amassed political power in Iraq. The American-led coalition accused him of organizing a 2007 attack that led to the deaths of five U.S. soldiers—he was subsequently captured and questioned. A report from June 18, 2007, interrogation claims Khazali told U.S. officials that training and arms were provided by Tehran to Shiite militias so they could attack U.S. forces and pressure them to leave Iraq. The report says Iranian officers didn’t dictate which specific targets should be attacked, but suggested that militias focus some of their attacks on British troops “to force a withdrawal” and increase pressure on the U.S. to withdraw as well. Khazali has previously publicly insisted that he is not beholden to Iran; Iran has long denied U.S. claims that it instigated instability in Iraq.