There are conflicting reports about the fate of a Shia militant leader of the Iraqi group which kidnapped five Britons in Baghdad in 2007, BBC reported.
Iraq's interior ministry said Qais al-Khazaali was freed, but Iraq's chief hostage negotiator Sami al-Askari later said the reports were "baseless".
Khazaali is said to be from the Asaib al-Haq group which seized Peter Moore and his four bodyguards in May 2007.
Mr Moore was freed last week. Three of the four guards were shot dead.
Their bodies were returned last year.
The fourth guard is also believed to have been killed.
Khazaali's release was always top of Asaib al-Haq's demands, the BBC's security correspondent Frank Gardner says.
Militants wanted a straight prisoner swap, but the US military held onto him because he was suspected of being involved in a raid that killed five US servicemen in 2007, our correspondent adds.
Several militants had already been handed to the Iraqi government and some had since been freed under the reconciliation process.
The five Britons were captured at the Iraqi Ministry of Finance by about 40 men disguised as Iraqi policemen in May 2007.
Mr Moore, aged 36, had been working for US management consultancy Bearingpoint in Iraq. The other men were security contractors employed to guard him.
Mr Moore was in good health after his release last week, British officials have said.
The bodies of Jason Swindlehurst, from Skelmersdale, Lancashire, and Jason Creswell, of Glasgow, were returned to the UK in June 2009, followed by that of fellow bodyguard Alec MacLachlan, of Llanelli, Carmarthenshire, in September.
The fourth guard, Alan McMenemy from Glasgow, is also thought to have been killed. Foreign Secretary David Miliband has called for the release of his body.