BAGHDAD, Iraq - Two high-profile women prisoners in American custody will not be released immediately, the U.S. Embassy said, despite an earlier announcement by Iraqi authorities promising to free one woman.

The two female scientists "are in our legal and physical custody," a U.S. Embassy spokesman said today.

"Legal status of these two and many others is under constant review," he said.

Militants say they have beheaded two American hostages and have threatened to kill a British captive unless Muslim women in U.S. custody in Iraq are freed.

The U.S. military says the only two Iraqi women in its custody are two security prisoners being held at an undisclosed location - Rihab Rashid Taha, a scientist who became known as "Dr. Germ" for helping Iraq make weapons out of anthrax, and Huda Salih Mahdi Ammash, a biotech researcher known as "Mrs. Anthrax."

A Justice Ministry spokesman had announced that Iraqi authorities together with U.S.-led forces had decided to release Taha on bail.

Ministry spokesman Noori Abdul-Rahim Ibrahim denied the decision was linked to the militants' demands.

"The Iraqi authorities have agreed with coalition forces to conditionally release Rihab Rashid Taha on bail," Ibrahim said. "The decision ... has nothing to do with the threat made by the kidnappers."

Ibrahim said authorities were also considering whether to release Ammash, saying her case was "under study."

Taha is the wife of Amer Mohammed Rashid, who surrendered to coalition forces in April. He was No. 47 on the most-wanted list and had been Saddam's missile expert.

Tawhid and Jihad, an al-Qaida-linked group led by Abu Musab al-Zarqawi, snatched the two Americans and the Briton last week. It released a video showing the beheading of one of the Americans on Monday and the following day announced it had killed the second.

The first American's body was found and identified. Another decapitated body was found in Baghdad today and authorities are trying to confirm whether it is the other American's.

Relatives of the British hostage, Kenneth Bigley, pleaded with British authorities to intervene to win the release of women prisoners in a bid to meet the militants's demands and save Bigley's life.

"The release of the two high value detainees is a matter for the U.S. and Iraqi authorities," a spokeswoman for the British Embassy in Baghdad said: "It is not a process in which we are involved."

"Our primary aim is to save the life of Kenneth Bigley," she said, adding that there are no female detainees held by British troops in Iraq.

Hensley and fellow American Eugene Armstrong were kidnapped Thursday with Bigley from a home that the three civil engineers shared in an upscale Baghdad neighborhood. Al-Zarqawi beheaded Armstrong, and the militants on Monday posted a gruesome video of the 52-year-old man's death.

Meanwhile, U.S. aircraft and tanks attacked rebel positions in Baghdad's Sadr City slum today, killing 10 people and wounding 92, hospital officials said. And a suicide attacker detonated a car bomb outside a photocopy shop in western Baghdad where Iraqi National Guard applicants prepared papers before heading to a nearby recruiting center, killing at least six people and wounding 54, authorities said.

The fighting came as U.S. and Iraqi forces searched for weapons caches in Sadr City, a Shiite stronghold. An Associated Press reporter near the scene said a U.S. C130 gunship raked one area with heavy fire after rebels loyal to radical Shiite cleric Muqtada al-Sadr opened fire with rocket propelled grenades.