The U.S. military said the Iraqi security unit, which was not identified, came under fire and shot back in self-defense. Relatives and neighbors say troops set off explosives that knocked down the gates and doors to a home, detained an Iraqi military intelligence officer and killed two civilians. Their bodies were discovered with dog bites and gunshot wounds on a kitchen floor, which was streaked with blood, the witnesses said. What actually happened might never be known. The starkly different accounts underscored the volatile atmosphere in Baghdad, where multiple security branches operate, often in secrecy, and armed groups hide among the civilian population. It was not immediately clear which Iraqi security branch -- special forces, an elite police unit or regular infantrymen -- took part in the raid. Iraq's counter-terrorism branch, which commands the special forces, denied any involvement. A spokesman for the Iraqis' Baghdad operations command did not respond to requests for comment. The U.S. military released a statement Wednesday night. 'Iraqi security forces conducted a security operation in southeastern Baghdad Wednesday,' it read. 'During the operation, the force was fired upon by two individuals in a nearby building. In self defense, the force immediately returned fire and killed the two aggressors.' On Wednesday, neighbors and relatives gathered near the cinnamon-colored home, with its smashed-in gate and door. They had their own account of what happened in Zafraniya's Muwalamin Ula section, home to Sunni Arabs and Shiite Muslims. Abu Haitham, a 50-year-old resident on the same street, said he had been awakened before dawn by an Iraqi police vehicle that announced U.S. and Iraqi forces had sealed off the area and people should not leave their homes. He said he saw military vehicles outside his window and that his home was shaken by three large explosions, accompanied by the sound of women and children screaming. After the forces left, Abu Haitham said, he went to the house that had been raided and was among the first to see the dead. 'One of the bodies had been badly mutilated; even dogs had bitten it,' said the man, who did not give his full name for fear of retribution. 'This is a brutal way. If they have something against the guy, they should detain him and interrogate him, not like this.' Relatives pointed to the kitchen and backyard, both streaked with a trail of blood and mottled with congealed black spots, and a bullet hole in the yard and similar marks in the kitchen. One man, who identified himself as the brother of the arrested suspect, insisted that his family was innocent. He said his brother, Nasr Rashid Abed Nasaif, was a warrant officer in the 11th Iraqi Army Division. He described the family as Sunni. 'Did they come here to detain an al-Qaida leader? Believe me, if we thought that they were involved in something suspicious we would be the first to tell on them. But they are innocent people, and my brother is serving the country,' said the man, who called himself Abu Mustafa. The dead men were identified as Mohammed Jassim Ahmad Karkhi, a resident of the house where the shooting occurred, and Abu Kara, a friend who was staying overnight after sharing iftar, the sunset meal at which Muslims break their daylong fast during the holy month of Ramadan. Karkhi's sister, who requested anonymity, said her family fled the northeastern city of Baqouba during sectarian fighting in recent years and had moved in with relatives in Zafraniya. Her slain brother and another sibling had been detained by Iraqi special forces for 16 days last year, she added. 'We are people who were displaced, and my father died because we lost our home, and now they took my brother's life,' she said, her voice rising. 'There must be a secret informant who passed them false information.' 