DUBAI, United Arab Emirates -- The brother of a British hostage in Iraq said his family has seen "absolute proof" that the hostage -- Kenneth Bigley -- is dead.

"The family here in Liverpool believe that our government did everything it possibly could to secure the release of Ken in this impossible situation. It could be that the fate of Ken, Eugene and Jack were sealed from day one. We will never know," the slain man's brother, Phil Bigley, said.

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Rundown: Info About Kidnappings In Iraq

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But in a separate statement, another Bigley brother criticized Prime Minister Tony Blair over the Iraq war -- saying, "Please, please stop this war and prevent other lives being lost."

A videotape reportedly shows British hostage Bigley being beheaded by kidnappers in Iraq.

A witness who saw the tape said it shows six armed and hooded men standing behind Bigley, who is kneeling. One of the men spoke in Arabic -- and then took a knife from his belt and severed Bigley's head. The witness says the tape ends with the killer holding up the severed head.

The man who is seen killing Bigley said it's because the British government didn't meet demands to free Iraqi women.

Bigley's wife is from Thailand and made many emotional pleas to the kidnappers. Bigley was kidnapped just weeks before he planned to retire from his work in Iraq. He had planned to return to Thailand and live with his wife.

Blair has voiced his "utter revulsion" for Bigley’s killers. Blair spoke Friday on national television, after news surfaced of a new videotape showing Bigley being beheaded. Blair said he hoped that such "barbaric" actions would not dissuade others from trying to rebuild Iraq -- as Kenneth Bigley had sought to do.

Both Blair and British Foreign Secretary Jack Straw offered Bigley's family condolences -- and Blair praised them for their "dignity and courage."

Earlier, Straw said the British government had exchanged messages with Bigley's captors in an effort to win his release.

Meanwhile, U.S. military officials in Iraq said they have not found a body they believe is Bigley's.

The reports of Bigley's decapitation came a day after Iraqi Prime Minister Ayad Allawi hinted progress was being made to free Bigley.

Kidnappers have abducted more than 150 people in Iraq this year. At least 27 of them have been killed.

Bigley, 62, a British civil engineer, and two Americans were snatched from their Baghdad home Sept. 16. Both Americans were also beheaded. Jack Hensley, 48, and Eugene "Jack" Armstrong , 52, were killed over two weeks ago. Hensley's beheaded body was found Sept. 22 and and Armstrong's body was found Sept. 20.

Two videos had earlier surfaced in which Bigley pleads with Blair to save his life by meeting the demands of his kidnappers.

On Sept. 29, a videotape aired on Arab news network Al-Jazeera showed a sobbing Kenneth Bigley, talking from behind bars in what appeared to be a prison cell. Bigley was dressed in an orange jumpsuit, and was kneeling on the floor. He was pleading to Blair to work for his release.

Before that, Bigley appeared on a videotape posted on an Islamic Web site weeping and pleading for Blair to help save his life.

"To Mr. Blair, my name is Ken Bigley, from Liverpool," the blindfolded man said in the videotape.

"I think this is possibly my last chance," the speaker said in the grainy video. "I don't want to die. I don't deserve."

"Please free female prisoners held in Iraqi prisons," he also said.

Tawhid and Jihad, the militant group led by Jordanian terrorist mastermind Abu Musab al-Zarqawi, had threatened to kill Bigley unless Iraqi women held in U.S. custody were released.