Mr. Daqduq, who was captured by British forces in Basra in March 2007, was the last detainee to be handed over to the Iraqis by the United States as American troops withdrew in December 2011.

American military officials have accused Mr. Daqduq of working with the Quds Force — an Iranian paramilitary unit that supports militant movements abroad — to train Shiite militias in Iraq during the war. One of the most serious allegations stems from his suspected role in helping to organize a January 2007 raid in Karbala that led to the deaths of five American soldiers…

“The United States continues to believe that Daqduq should be held accountable for his crimes,” said a State Department official, who asked not be identified because he was discussing a delicate diplomatic issue. A spokeswoman for the National Security Council declined to comment.

Mr. Daqduq, a member of Hezbollah since 1983, once supervised the security detail for Hassan Nasrallah, Hezbollah’s supreme leader.