'A truly barbaric act'

Downing Street today led condemnation of the video execution of an American businessman by militants linked to al Qaeda.

Tony Blair's official spokesman said of the film of Nick Berg's killing: "This was a truly barbaric act and there is no justification for this kind of act in a civilised world."

The White House has offered a £6 million reward for the capture of Abu Musab al-Zarqawi, a senior lieutenant of Osama bin Laden.

Zarqawi claimed the credit for the murder of the 26-year-old civilian whose execution was filmed and broadcast on the internet. Five masked men chant "God is greatest" as one of them produces a knife. Mr Berg is kneeling in front of them.

A scream is heard before his head is cut off and held before the camera. The group said the execution was in revenge for the abuse of Iraqi prisoners by US soldiers.

"It shows the true nature of the enemies of freedom," said the President's spokesman Scott McClellan. But in a bitter twist to the crisis engulfing the United States, the family of Mr Berg blamed the President for the tragedy. It emerged that their son had been trying to get out of Iraq but was held for questioning by the US military for two weeks.

When he was finally released it was too late for him to leave safely, his family said.

The al Qaeda linked website on which the murder video was posted specifically names Zarqawi, saying he was "shown slaughtering an American".

The tape shows Mr Berg identifying himself while dressed in an orange jumpsuit, apparently in a deliberate attempt to make him look like Iraqis being held in US custody.

His death is seen as the first retaliation by Muslim extremists for the photographs of Iraqis being tortured and sexually humiliated at the Abu Ghraib prison in Baghdad.

Zarqawi is an expert in chemical and biological weapons and is already wanted for dozens of killings. Intelligence agencies link him with the recent bombings in Casablanca, Istanbul, and Madrid and say he is wanted for the murder of US diplomat James Foley two years ago.

He is understood to be commander of Ansar al-Islam, a Kurdish guerrilla organisation active in northern Iraq before the fall of Saddam Hussein. Zarqawi, who is of Palestinian descent, is also suspected of masterminding bomb raids on Shias in Kerbala and Baghdad.

He also claimed responsibility for suicide boat attacks that killed three Americans and disabled Iraq's biggest oil terminal for more than 24 hours last month.

Jordanian-born Zarqawi trained in the al Qaeda camps in Afghanistan for the war against Soviet occupation and became one of Bin Laden's senior lieutenants.

He was wounded during fighting against US troops in Afghanistan and had to have his leg amputated before finally seeking refuge in Iraq.

He was singled out by US secretary of state Colin Powell last March as proof that Saddam was harbouring al Qaeda terrorists .

As the world reacted in horror at the "barbarous" beheading, it emerged that Mr Berg had been held for two weeks in Iraq without charge by the US authorities.

By the time he was released, the worsening security situation had made it almost impossible to leave the country. Just three days after his release he was abducted by al Qaeda. "That's what really cost my son his life," said his father

Michael. The fact that the United States government saw fit to keep him in custody for 13 days without any of his due process or civil rights."

His son was a freelance contractor who turned up in Iraq looking for work and excitement. Unlike most involved in Iraq's reconstruction he did not have a job arranged in advance and lacked the protection of a big company as employer. Mr Berg arrived in Iraq on 21 December-and stayed until 1 February, making contact with a company that said it may have work for him later. He returned on 14 March but the hoped-for job was not on offer so he began travelling.

He usually called home once a day and emailed several times. On 31 March, FBI agents called at the family home in West Chester, Pennsylvania, and told his parents he was being held and interrogated about what he was doing in Iraq.

Six days later the family filed a lawsuit claiming their son was being held illegally by the US military in Iraq. Mr Berg was released by the coalition the next day, and told his family he would come home through Jordan, Turkey or Kuwait.