Former Australian prime minister Paul Keating has launched a ferocious attack on his successor John Howard, claiming his “craven” support of the American invasion of Iraq “visited on Australia the whole spectre of terrorism” and torched our multicultural society.

Keating said Howard’s “stubborn and unctuous denial of his responsibility” in committing troops to the assault “should be held in contempt by every thinking Australian”.

In an extraordinarily strongly-worded statement, he said that in light of the Chilcot report on Britain’s involvement in the war, Howard “should atone for his actions and those of his government. He should, at least, hang his head in shame”.

The Chilcot inquiry concluded the United Kingdom chose to join the invasion before the peaceful options for disarmament had been exhausted – military action was not the last resort.

Howard on Thursday stood by his own decision, based on the information at the time. “I defend it. I don’t retreat from it. I don’t believe, based on the information available to me, that it was the wrong decision. I really don’t.”

He said that over the years there had been the constant claim that we went to war on the basis of a lie. “There was no lie. There were errors in intelligence, but there was no lie.”

Keating said Howard had committed Australia, by his own admission, on the basis of Saddam Hussein having weapons of mass destruction. But there was never any evidence of such weapons and that was established following the exhaustive United Nations investigation led by Hans Blix.

The incompetent management of Iraq after the invasion fractured it and with it Syria and the region, casting millions of people adrift, he said. “A sea of refugees. Yet Howard has no shame of it. And no responsibility.”

Keating said that during Howard’s prime ministership, “his party was advertising that people should be aware of the risk of terrorism. And invited people to pin such official warnings on their fridges with magnets. We need more than magnets now”.

“Howard has visited on Australia the whole spectre of terrorism, through his craven and ill-judged support of the United States and its invasion.

“Australia was perhaps the most successful multicultural society in the world, including the settlement of a large Muslim population. John Howard put the torch to that,” Keating said.

“Now we live perpetually with the spectre of terrorism and racial strife, visited upon us by his prejudices and lack of judgment,” he said.