The Iraqi government has denied that moves to release a female prisoner is connected with demands made by militants holding a British man hostage.
Tonight, a video on a Islamist website showed Ken Bigley appealing to Tony Blair to save his life.
Earlier, Iraq's National Security Advisor said a female prisoner whose release has been demanded by the militants will be set free soon.
Kassim Daoud told a news conference the release of Rihab Rashid Taha would be conditional and would not happen for a few days.
Ms Taha was a biological weapons scientist during Saddam Hussein's rule.
Her release has been demanded by militants holding a British hostage who have already executed two Americans. They are also demanding the release of a second female scientist.
However, the US embassy in Iraq said both female prisoners are in the physical and legal custody of the US and will not be freed imminently.
Meanwhile, the US embassy in Baghdad has received a body from Iraqi authorities.
It has been identified as the body of Jack Hensley, who was kidnapped last Thursday with two other colleagues who worked for the same UAE construction company. Another hostage, American engineer Eugene Armstrong, was killed on Monday.
The kidnappers are now threatening to kill 62-year-old British engineer Kenneth Bigley if the Iraqi women held in US-run prisons are not released.
Mr Bigley's brother, Paul, called on coalition forces to negotiate with the kidnappers. This follows an appeal yesterday by his family to the British Prime Minister, Tony Blair.
