In a statement to the UK-based movement, ahead of its anti-war demonstration in London on Saturday, Michael Berg said the US president George Bush's "ineffective leadership is a weapon of mass destruction".
"It has allowed a chain reaction of events that led to the unlawful detention of my son."
"Nick took the consequences of the policies both stated and given with a wink and a nod by the Bush administration."
Twenty-six-year-old Nicholas' headless corpse was found in Baghdad on 9 May and a few days later, grainy footage of his execution was published on a website, which has now been shut down.
The US president, Berg stressed, "can see neither the heart of Nicholas nor the American people, let alone the people his policies are killing daily".
Berg, himself an anti-war proponent, again pointed fingers at the Federal Bureau of Investigation (FBI), saying it was the US government under whose authority his son was held.
"No one believes the Iraqi police controls the American FBI and military, Mr Bush."
"That detention immersed my son in a world of escalated violence, which, were it not for his detention, would have had him in my arms again."
The Berg family contend that their son had already intended to leave the country on 30 March but that his detention prevented him from doing so.
The grainy video of Berg's death
was shown on the internet
They say Nicholas was missing from 24 March until his release on 6 April.
He was released after the family sued in a Philadelphia federal court and named US Secretary of Defence Donald Rumsfeld as responsible for their son's disappearance.
He disappeared again on 9 April after telling his parents he was looking for a safe way out.
"That detention held him in Iraq not only until the atrocities that led to the siege of Fallujah, but to the revelation of the atrocities committed in the jails in Iraq in retaliation for which my son's wonderful life was put to an end," Berg adds in his statement, which will be read out at the demonstration.
Berg expressed frustration at the "lies from our government about Nick's detention".
"And we are fed up with the lies from our government about the reasons for this war."
President Bush's 'ineffective
leadership is a WMD' says Berg
Calling attention to the situation in occupied Palestine, Berg was adamant that the world wanted peace.
"So what were we to do when we in America were attacked on September 11, that infamous day?" Berg asked.
"I say we should have done then what we never did before: Stop speaking to the people we labelled our enemies and start listening to them."
He added: "Stop giving preconditions to our peaceful coexistence on this small planet, and start honoring and respecting every human's need to live free and autonomously, to truly respect the sovereignty of every state whether it be Israel, or Palestine or Iraq."
Stop making up rules by which others must live and then separate rules for ourselves, Berg said.
The Stop The War Coalition with the support of the Muslim Association of Britain have called for the emergency demonstration to demand an end to torture in Iraq and the withdrawal of troops from the country.
"Muslims around world, especially the MAB in Britain, are outraged and hurt at seeing our fellow brothers and sisters being tortured in Iraq, under the guise of supporting democracy and freedom in the Arab world," MAB spokesman Ihtishaam Hibat Allah told Aljazeera.net.
"We are calling on the British and American governments to let Iraq and other Arab countries decide their own future. Stop illegally occupying their country (Iraq)."