Former British PM Tony Blair both apologized and defended his actions on Wednesday in the wake of a damning report from the country's inquiry into the war in Iraq that said the conflict was mounted on flawed intelligence, executed with "wholly inadequate" planning and ended "a long way from success."

Retired civil servant John Chilcot, who oversaw the seven-year inquiry, said "the U.K. chose to join the invasion of Iraq before the peaceful options for disarmament had been exhausted. Military action at that time was not a last resort."

The 2.6-million-word report is an exhaustive verdict on a divisive conflict that, by the time British combat forces left in 2009, had killed 179 British troops, almost 4,500 American personnel and more than 100,000 Iraqis.

'I will be with you, whatever.' - Tony Blair, in a 2002 note to George W. Bush

Chilcot said then Prime Minister Tony Blair's government presented an assessment of the threat posed by Saddam Hussein's weapons with "certainty that was not justified." He also found military planning for the war and its aftermath were not up to the task.

"The people of Iraq have suffered greatly" because of a military intervention "which went badly wrong," he said. But he refrained from saying whether the 2003 invasion was legal, and did not find that Blair and his government knowingly misled Parliament or the British public.

Chilcot heard from 150 witnesses and analyzed 150,000 documents. His conclusions are a blow to Blair, who told President George W. Bush eight months before the March 2003 invasion — without consulting government colleagues — "I will be with you whatever."

IRAQ BRITAIN

A British solider sits near the North Ramala oilfields in Iraq in 2003. (Reuters)

'Failed to plan'

The report says Blair went to war to stand shoulder-to-shoulder with Britain's main ally, only to find the U.K. excluded from most important decision-making about the military campaign and its aftermath.

"Mr. Blair, who recognized the significance of the post-conflict phase, did not press President Bush for definite assurances about U.S. plans," the report concluded.

'I accept full responsibility without exception and without excuse.' - Tony Blair, on Wednesday

Iraq descended into sectarian strife after the occupiers dismantled Saddam's government and military apparatus, unleashing chaos that helped give rise to the Islamic State of Iraq and Syria (ISIS).

The report found failings by military chiefs who did not provide adequate equipment to forces in the field, and whose main post-invasion strategy "was to reduce the level of [U.K.] deployed forces."

The report concludes that Britain's combat mission, which ended in 2009, did not achieve the objectives laid out in 2003 and saw British forces make a "humiliating" deal with militias in southern Iraq to avoid attacks.

"The U.K. failed to plan or prepare for the major reconstruction program required in Iraq," the report said.

The war has overshadowed the legacy of Blair, whose government has been accused of exaggerating intelligence about Saddam's alleged weapons of mass destruction in order to build support for the invasion.

Britain Iraq Inquiry

John Chilcot presents the Iraq Inquiry Report at the Queen Elizabeth II Centre in London, on Wednesday. (Dan Kitwood/Associated Press)

Blair responds

Chilcot criticized spy chiefs who failed to ensure their partial intelligence about Saddam's weapons was not hardened into certainty by government spin. He said they also failed to consider "that Iraq might no longer have chemical biological or nuclear weapons" — which turned out to be the case.

The report said the widespread perception that the government had exaggerated intelligence evidence "has produced a damaging legacy, including undermining trust and confidence in government statements."

The report also faults Blair for making key decisions with only a few key aides rather than through collective Cabinet consultation.

Blair said he accepted responsibility for what happened in Iraq, but in a lengthy and emotional news conference said he stood by the decision to invade — insisting it seemed like the right move at the time and that the long-term "human cost" would have been worse if Saddam had remained in power. 

"Saddam was a wellspring of terror, a continuing threat to peace and to his own people," Blair said. "I believe he would once again have threatened world peace." 

Blair also said it was because of his insistence that the U.S. sought UN approval before going ahead with the invasion.

Blair's note to Bush in 2002 — in which he pledged his support "whatever" — said support from allies including Germany and France would likely rely on "specific UN authority." 

It also included cautionary language about potential fallout and complications, including the possibility that "real Iraqis, not Saddam's special guard" might "offer resistance." 

"If we win quickly, everyone will be our friend," Blair wrote. "If we don't … recriminations will start fast." 

Families react to Chilcot report0:54

In Parliament on Wednesday, Prime Minister David Cameron said those who supported the war, himself included, must take the "fair share of the blame." But he added it would be a mistake to dismiss the assessments of spy agencies as unreliable or to conclude that armed intervention is "always wrong."

Cameron cited the more successful interventions in Sierra Leone and Kosovo as examples.

"We cannot turn the clock back but we can ensure that lessons are learned and acted upon," he told MPs.

"Intervention is hard, but war fighting is not always the most difficult part. Often the state building that follows is a much more complex problem."

Chilcot's report has been repeatedly delayed, in part by wrangling over the inclusion of classified material, including conversations between Blair and Bush. Some of Blair's pre-war letters to the president are published in Chilcot's report, but not Bush's replies.

Anti-war activists and relatives of some dead British troops hoped the report would find the conflict illegal, opening the way for Blair to be prosecuted for war crimes.

The International Criminal Court is looking into alleged war crimes by British troops in Iraq, but has said that Britain's decision to go to war falls outside its jurisdiction.

Bushs Language

U.S. President George W. Bush, right, appears with British Prime Minister Tony Blair at the White House in 2007. (Charles Dharapak/Associated Press)

With files from CBC News