Violent insurgency in Iraq is the “predictable” result of the West’s failure to intervene in Syria, not of the 2003 invasion to topple Saddam Hussein, Tony Blair has declared in a renewed call for military action.
The former prime minister’s intervention in the debate comes amid international moves to tackle the bloody insurgency by Islamist extremists and deal with its humanitarian consequences.
Thousands have fled the sweeping advance of fighters from the al-Qaida-inspired Islamic State of Iraq and the Levant (Isis), who have taken control of large areas including second city Mosul.
US president Barack Obama is considering a range of military options - said to include air strikes - over the coming days.
Meanwhile Iran - a key ally of Nouri al-Maliki’s Shia-dominated administration in Baghdad - indicated that it was ready to provide assistance.
Iranian president Hassan Rouhani said his country had “no option but to confront terrorism” and was “ready to provide assistance within international law” if requested.
And Britain is to give £3 million of aid to Iraq. International Development Secretary Justine Greening said the initial tranche of emergency cash would allow agencies to supply water, sanitation, medicine, hygiene kits and basic household items.
Mr Blair rejected as “bizarre” arguments that Iraq would be more stable and peaceful today if the US-backed war, which claimed the lives of 179 UK personnel, had not happened.
He said that unless the international community was prepared to overcome public reluctance and confront the extremists “hard, with force”, the consequences would be more serious still.
Mr Blair - now a Middle East peace envoy - said Iraq was “in mortal danger” but pinned the blame on the sectarianism of the Maliki government and the spread of Syria’s brutal three-year civil war.
He hit back at critics of the controversial war in an eight-page essay on his website, saying al-Qaida had been a “beaten force” in Iraq as recently as three years ago, but the chance of peace was squandered by Baghdad.
“By all means argue about the wisdom of earlier decisions,” he wrote.
“But it is the decisions now that will matter.
“The choices are all pretty ugly, it is true. But for three years we have watched Syria descend into the abyss and as it is going down, it is slowly but surely wrapping its cords around us, pulling us down with it.
“We have to put aside the differences of the past and act now to save the future.
“Where the extremists are fighting, they have to be countered hard, with force.”
It did not mean another invasion, he said.
“There are masses of responses we can make short of that. But they need to know that wherever they’re engaged in terror, we will be hitting them.”
He said the Iraq assault had been planned and prepared in the Syria conflict zone and was the “predictable and malign effect” of allowing that situation to be exploited by extremists.
Air strikes against the Assad regime had been on the table last summer over its use of chemical weapons but a Commons vote against the idea helped end the prospect of action.
“I understand all the reasons following Afghanistan and Iraq why public opinion was so hostile to involvement,” Mr Blair wrote.
“Action in Syria did not and need not be as in those military engagements. But every time we put off action, the action we will be forced to take will be ultimately greater.”
He wrote: “The moderate and sensible elements of the Syria opposition should be given the support they need; Assad should know he cannot win an outright victory; and the extremist groups, whether in Syria or Iraq, should be targeted, in coordination and with the agreement of the Arab countries.
“However unpalatable this may seem, the alternative is worse.”
Ms Greening said that Iraq is facing “serious humanitarian need”.
She added: “The UK contribution to the international relief response will include initial funding for clean water, medicine and sanitation, as well as support for the UNHCR (the United Nations refugee agency) to provide dedicated safety and welfare teams to protect vulnerable women.”
Two thirds of the aid money will be used by NGOs in the region to supply clean water and sanitation, essential medicine, women-friendly hygiene kits and basic household items, the DfID said.
The rest would help protect vulnerable girls and women by funding dedicated UN safety and welfare teams to refugee camps.
Sir Christopher Meyer, who was Britain’s ambassador to the US from 1997 to 2003, said Mr Blair was wrong and that the handling of the campaign against Saddam was “perhaps the most significant reason” for the sectarian violence now ripping through Iraq.
“There are many reasons for this disastrous state of affairs,” he wrote in the Mail on Sunday. “Perhaps the most significant is the decision taken more than 10 years ago by President George W Bush and Prime Minister Tony Blair to unseat Saddam Hussein without thinking through the consequences for Iraq of the dictator’s removal.”
The decision to bar members of Saddam’s Ba’ath party from top jobs and disbanding the army - one former member of which now leads the Isis surge, were among the most serious errors, he said.
“We are reaping what we sowed in 2003. This is not hindsight. We knew in the run-up to war that the overthrow of Saddam Hussein would seriously destabilise Iraq after 24 years of his iron rule.
“For all his evil, he kept a lid on sectarian violence. Bush and Blair were repeatedly warned by their advisers and diplomats to make dispositions accordingly.
“But, as we now know, very little was done until the last minute; and what was done... simply made things far worse.”
Clare Short, former International Development Secretary who resigned her post in 2003 over the Iraq war, said Mr Blair had been “absolutely, consistently wrong, wrong, wrong” on the issue, and branded him a “complete American neocon”.
Speaking on the Murnaghan programme on Sky News, she criticised the “deceit” over the decision to invade, and added: “More bombing will not solve it, it will just exacerbate it.”
Asked about Syria, she replied: “Who are you going to bomb?... Remember Northern Ireland. When there is an uprising backed by some of the people, if you bomb you kill some of the people and make the people more angry and strengthen the forces of opposition.
“I agree we have been wrong in Syria - but we have been wrong by wanting to get rid of Assad rather than help the people of Syria and that’s because we are focused on being hostile to Iran.
“We won’t get any solutions in Iraq or Syria without being allies of Iran. Iran indeed has offered help because of course these extreme forces hate the Shia and are killing them.”
Alistair Burt MP told the same programme that there was a “great danger” of trying to understand the situation by getting back to just one root cause.
He called for a group of moderate Arab states to come together to tackle the problem, which he said could not be done by the West.
Shadow foreign secretary Douglas Alexander insisted the Iraqis themselves hold the key to resolving the crisis, and called on the country’s prime minister to act.
He said: “Notwithstanding the sacrifices that Britain has made for Iraq in past years - including the lives of 179 brave members of our Armed Forces - the truth is that it is the Iraqis themselves who hold the key to resolving this crisis.
“Iraq’s prime minister Nouri al-Malaki has so far been unwilling or unable to do what is needed for his country and its people.
“But with the militant threat marching towards Baghdad, he must now act to deliver a strong Iraqi military response alongside a united and determined political front.
“The most urgent task is to unite Iraq and galvanise its response to this crisis - the future of a whole country and the fate of millions of its citizens depends upon it.”