Jeremy Corbyn: Iraq invasion was a 'catastrophe'
The 2003 Iraq invasion was "an act of military aggression" and a "catastrophe", Labour leader Jeremy Corbyn said.
Responding to the publication of Sir John Chilcot's inquiry into the war, Mr Corbyn said MPs had been "misled" in the run-up to the invasion.
He also apologised on behalf of Labour and called for more powers for the International Criminal Court.
David Cameron said lessons must be learned from the Iraq War.
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He announced a two-day Commons debate into Sir John's long-awaited report.
Sir John said his report does not make a judgement on the legality or otherwise of the war.
But Mr Corbyn, a long-term critic of the war who voted against the invasion, said it had "long been regarded as illegal by the overwhelming by the weight of international legal opinion".
It "devastated Iraq's infrastructure" he said, and "fostered a lethal sectarianism".
"By any measure, the invasion and occupation of Iraq... has been for many a catastrophe," he said.
Going to war without a UN mandate was "profoundly dangerous", Mr Corbyn said, adding: "All those who took the decisions laid bare in the Chilcot report must face up to the consequences of their actions, whatever they may be."
He paid tribute to the late Robin Cook, who resigned from the government over his opposition to the war.
Mr Corbyn said that in his resignation speech, Mr Cook had said "in a few hundred words in advance of the tragedy to come what has been confirmed by this report in more than two million words".
In a speech later on, Mr Corbyn apologised to Iraqis, soldiers' families and Britons who feel democracy was "undermined" by the invasion.
He said: "Politicians and political parties can only grow stronger by acknowledging when they get it wrong and by facing up to their mistakes.
"So I now apologise sincerely on behalf of my party for the disastrous decision to go to war in Iraq."
He added: "Finally, we need Britain to join the 30 countries including Germany and Spain that already support giving the International Criminal Court the power to prosecute those responsible for the crime of military aggression."
Earlier, as he fielded questions from MPs, Mr Cameron, who as a backbencher at the time voted in favour of intervention, said: "Members on all sides who voted for military action will have to take our fair share of the responsibility.
"We cannot turn the clock back but we can ensure that lessons are learned and acted on."
He said the experience of Iraq should not prevent Britain from collaborating with the United States in future military action.
Lib Dem leader Tim Farron said the late Charles Kennedy, who led his party at the time had been "right all along" in his opposition.
Labour MP Ann Clwyd said Saddam Hussein had been in breach of UN resolution and killed thousands of his citizens.
She said: "I wish people would ask Iraqis what they think of the invasion, because many are grateful that we took the action that we did at that time."