A militant group affiliated to al-Qaida in Iraq said in a new video released on Monday that its militants had killed three American soldiers who they captured in mid-May.

The group, called the Islamic State of Iraq, said in the video that it decided to announce the Americans' killing, "which makes a bitter result ... because they were alive and then dead."

The three U.S. soldiers were captured south of Baghdad on May 12 after a deadly ambush on their patrol, which also claimed lives of five other U.S. soldiers.

The three later were identified by the U.S. military as Private first Class Joseph Anzack, 20, Private Byron Fouty, 19, and Specialist Alex Jimenez, 25.

The video lasted nearly 11 minutes, which showed a group of masked men involved in the ambush and nighttime footage, which the group said was the ambush that led to the soldiers' capture.

The video also showed identification cards for both Fouty and Jimenez.

The speaker in the video also blamed the deaths of the three U.S. soldiers on "the American army and their leaders, who never care for the feelings of the soldiers' mothers."

The video release came several days after the U.S. army said that Anzack's body was found floating in Iraq's Euphrates river and it was still searching for the other two soldiers.