BAGHDAD, Iraq - Authorities insisted they won't give in to militants' demands to free female Iraqi prisoners despite the broadcast of a videotape that showed a tearful British hostage begging Britain to save his life.

The captive, Kenneth Bigley, appealed to British Prime Minister Tony Blair to intervene. "I think this is possibly my last chance," he said. "I don't want to die."

Bigley's brother, Paul, accused the United States of sabotaging efforts to save his brother's life. He told the British Broadcasting Corp. on Thursday that his hopes were raised when Iraqi ministers said one of the female prisoners would be freed. But soon afterward, a U.S. Embassy spokesman ruled out any immediate release.

"That was a shadow of light in a big, long, dark, damp, filthy, cold tunnel. Now this has been sabotaged," he said.

On Wednesday, an Internet statement purportedly by a group which claimed to have kidnapped two Italian aid workers in Iraq said it had killed the women. The pair were working for "Un Ponte Per ..." ("A Bridge to ...").

A second militant group claimed today in a Web posting that the two Italian women had been killed. The second statement promised that a video of the slayings would be released. Neither claim could be immediately verified.

Simona Pari and Simona Torretta, both 29, were seized from their Baghdad offices by armed militants on Sept. 7. They worked for and were involved in school and water projects in Iraq.

The first claim they were killed was unusual because it appeared on a Web site not regularly used by Iraqi militants to relay their statements. A source close to Italian Premier Silvio Berlusconi said the government suspected the claim might not be credible.

Bigley was being held by a militant group led by Jordanian-born terror mastermind Abu Musab al-Zarqawi. The group has already beheaded Americans Eugene Armstrong and Jack Hensley, whom it abducted along with Bigley from the Westerners' Baghdad home last week. The militants demanded the release of all female prisoners in Iraq.

On Wednesday, the group also posted a video of Hensley's killing on the Internet, as it had two days earlier of Armstrong's beheading.

The gruesome hostage drama played out as fighting raged on in Iraq. At least 20 people - including three U.S. soldiers - were killed and more than 100 wounded.

Suicide attackers struck key diplomatic and commercial centers of the capital, and American tanks and troops searching for weapons stormed into the slum of Sadr City, a stronghold of Shiite militants - only to come under a barrage of mortar and automatic weapons fire. The violence underscored the inability of U.S. and Iraqi forces to bring security to even the most vital areas of the capital.

Fighting in Sadr City flared anew today, with U.S. warplanes firing on insurgents, killing at least one person and injuring 12, many of them children, hospital officials said.

U.S. warplanes and helicopters roared overhead and residents said loud explosions could be heard for hours. Militia fighters returned fire with machine guns, they said.

Earlier, a dispute broke out over the fate of female detainees when the Justice Ministry announced that Rihab Rashid Taha, a scientist who became known as "Dr. Germ" for helping Iraq make weapons out of anthrax, would be freed in the coming days because she was no longer a threat to national security.

Taha and another high-value detainee, Huda Salih Mahdi Ammash, a biotech researcher known as "Mrs. Anthrax," are the only two women the United States says it is holding.

But U.S. and Iraqi officials quickly found themselves at odds over who had custody over the pair, with Iraqi national security adviser Qassim Dawoud saying they were in the hands of Iraqi security forces and that "Iraqi judges decided to release them because they didn't have any evidence."

A U.S. Embassy spokesman disagreed, saying the two "are in our legal and physical custody."

Dawoud sought to clear up the matter today, saying the two sides were jointly reviewing the status of prisoners, including that of Taha - but not Ammash.

He insisted that the timing of the review and the demands by al-Zarqawi's group to free female prisoners - presumed to mean the two scientists - was a coincidence.

"There is no question of the Iraqi government or multinational forces changing these decisions in the light of the demands of a terrorist group which has taken three hostages and criminally and barbarically murdered two of them," Dawoud said in a statement.

The conflicting U.S. and Iraqi statements raised questions over who has authority in the country, even after the handover of sovereignty to Allawi's interim government in June. U.S. officials have been saying that they have been giving more decision-making power to Iraqis, including security matters.

Although Taha may well walk free in coming weeks or months, officials were determined not to be seen as giving in to the hostage takers' demands.

The group warned in a Web statement Wednesday that Bigley, 62, would be the next to die unless all Iraqi women are released from jail - though it did not set a deadline as it has in past statements.

In Wednesday's video, Bigley said Blair was the only man who could keep his kidnappers from killing him.

"Mr. Blair, I am nothing to you. Here's just one person living in the United Kingdom, that's all, with a family like you, like your family, your children, your boys, your wife," the speaker said in the grainy video.