The father of Nick Berg - the US civilian beheaded in Iraq - has sent a message of support to the Stop the War Coalition.
Mr Berg blames the US administration for his son's death
Michael Berg contacted the coalition to offer his backing after it sent him a letter of sympathy.
His strongly-worded message will be read out at an anti-war demonstration in London on Saturday.
Mr Berg said that his son had suffered the consequences of policies of the Bush administration.
Mr Berg said: "When I eulogized my son, Nick, I said that he was my teacher and my hero.
"He was the kindest, gentlest human being I know or have ever known."
Last year hundreds of thousands marched against the war
His son's headless corpse was found on 9 May in Baghdad and days later a video of his decapitation appeared on an al-Qaeda related website.
The hooded men who carried out the killing claimed they were avenging the abuse of Iraqi prisoners at Abu Ghraib.
The Stop the War Coalition will release Mr Berg's full statement at a press conference on Wednesday.
One of the march's organisers Chris Nineham told the BBC: "He [Mr Berg] feels that what needs to come out of the horrific death of his son is that a message has to be sent to Bush and Blair to say that the barbarity of war has to stop.
"That's his response to the terrible events that have happened to his son.
He continued: "I think the fact that someone has responded so thoughtfully to the death of their son is a message to the people of America and elsewhere to say that we understand that violence breeds violence.
"That violence was originally perpetrated by the American government, the British government and by the military and the only way to end the cycle of violence is for the US and British troops to come out immediately."
The Stop The War Coalition with the Muslim Association of Britain and CND have called for the emergency demonstration this Saturday to demand an end to torture in Iraq and the withdrawal of troops from the country.
A total of 200 anti-war protesters protested outside a Republican fundraising dinner in central London on Tuesday night attended by former US president George Bush senior.
Glasgow Kelvin MP Mr George Galloway was among the Stop the War coalition demonstrators.
Saturday's march will be the latest in a series of protests by the coalition against the Iraq conflict.