Three Turkish hostages held in Iraq have been released, according to the Arabic television station Al Jazeera.
The station earlier broadcast a videotape showing what militants said was the execution of a US soldier.
The US-led coalition yesterday handed powers to Iraqi leaders yesterday, two days earlier than planned, in an apparent effort to thwart any attempt to mark the event with a spectacular attack by militants. The low-key ceremony took many by surprise.
The day passed with no major incident on the streets. But video footage broadcast hours after the handover on Al Jazeeratelevision showed film of what a militant commentary said was a US soldier.
A gunman could be seen firing one shot at the soldier, wearing greenish overalls and seen only from the back. The body collapsed into a hole.
US defence officials said the family of Private Keith Matthew Maupin (20), seized by militants in April, had been told about the existence of the video but that there was no confirmation Mr Maupin, from Batavia, Ohio, was the man killed.
In a video aired after his capture in April, Mr Maupin told the camera: "My name is Keith Matthew Maupin. I am a soldier from the 1st Division. I am married with a 10-month-old child. I came to liberate Iraq, but I did not come willingly because I wanted to stay with my child".
Al Jazeeratoday quoted a statement from a previously unheard of group as saying the soldier was killed because of US policy in Iraq and in revenge for what it described as their "martyrs" in Iraq, Saudi Arabia and Algeria.
The group was identified as the Implacable Power Against the Enemy of God and the Prophet.
Since April, militants in Iraq have seized a number of foreign workers and military personnel. The three Turkish hostages had been threatened with execution today if Turkey did not order companies to stop dealing with US forces in Iraq. Ankara rejected the guerrilla demands. According to Al Jazeera, the militants holding the Turks said they were being freed "for the sake of Muslims".