(CNN) -- The family of Ken Bigley, the British engineer who was taken hostage in Iraq three weeks ago, has confirmed that he has been killed.
"We can confirm that the family has now received absolute proof that Ken Bigley has been executed," Phil Bigley said in a televised statement Friday.
He added the British government "did all it could to secure the release of Ken."
U.S. officials believe Bigley was beheaded by his captors after an escape attempt, U.S. and diplomatic sources told CNN on Friday.
They would not explain how they came to that conclusion but added that other people may have been killed -- possibly some of the captors who may have tried to help Bigley, or other hostages being held by the same group.
The officials said they do not know whether a rescue attempt was under way at the time
British Prime Minister Tony Blair, in a taped statement Friday, expressed his "utter revulsion" for the killers and said such actions "in Iraq or elsewhere should not prevail."
Foreign Secretary Jack Straw, speaking to reporters earlier Friday, condemned the killing as "barbaric murder."
He also revealed that British officials had exchanged messages with Bigley's captors in the past four days but "at no stage did the kidnappers abandon their demands."
Bigley, 62, was kidnapped from his Baghdad residence three weeks ago with two American colleagues, Jack Hensley and Eugene Armstrong.
The two Americans were subsequently beheaded and a video released showing the killings.
The Islamic militant group Unification and Jihad claimed to have kidnapped the men. It claims allegiance to terrorist mastermind Abu Musab al-Zarqawi.
Al-Zarqawi's group had demanded the release of all female Iraqi prisoners.
However, the International Committee of the Red Cross has insisted that Britain was not holding any women in Iraq.
Earlier Friday, the Reuters news agency reported that it had seen a video showing the beheading of a man, identified as Bigley.
The video showed Bigley surrounded by six militants, one of whom decapitates him, Reuters says.
Bigley was wearing an orange jumpsuit, the kind that has been worn by other hostages held in Iraq, as well as inmates of the U.S. detention center in Guantanamo Bay, Cuba.
The news came in the wake of international efforts by family members, politicians and Muslim leaders to save Bigley's life.
Paul Bigley, another brother of the hostage and a resident of Amsterdam, had been at the forefront of efforts by the family to free the hostage.
On Friday, in a statement to activists against the Iraq war issued after he had heard reports of his brother's death, Bigley said: "Please, please stop the war and prevent other lives being lost. It is illegal, it has to stop. Mr. Blair has blood on his hands."
On Wednesday, Libyan leader Moammar Gadhafi appealed to the kidnappers to release Bigley, Libya's official JANA news agency said.
One day earlier, Gadhafi's son, Saif, said his charity group was hoping to help secure Bigley's release.
Also Tuesday, Ireland issued a passport for Bigley in the hopes it would help secure his freedom.
Ireland is a neutral nation and has opposed the U.S.-led war in Iraq. (Full story)
The British government, a strong supporter of the war, had said it would listen to the kidnappers holding Bigley. But Straw, the foreign minister, maintained the government was not prepared to negotiate with them or pay them a ransom.
Two weeks ago, Muslim leaders from Britain traveled to Iraq to meet with their counterparts there and attempt to make contact with the kidnappers.
Akbar Ali, a Muslim leader in Liverpool who had appealed for the release of Bigley, told the UK's Press Association: "I think I can speak on behalf of all Muslims. We are very sad, we were all hoping he would be reprieved and representations had been made.
"This group are very, very ruthless people without aims or objectives, just trying to show the world how cruel and mindless they can be. They are giving a very, very negative picture of Islam."
Last week, an Arabic-language news channel broadcast a video showing Bigley caged behind bars.
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Postscript, another victim of senseless, beastly, inhuman voices which are like viruses multiplying.Very sad.