Military investigators have determined "battle fatigue" on the part of peshmerga fighters played a key role in the friendly fire accident that killed a Canadian special-forces soldier earlier this year in northern Iraq.

Canada's top military commander, General Tom Lawson, speaking during Prime Minister Stephen Harper's surprise tour of Iraq and Kuwait this weekend, said a series of probes have found Canadian soldiers were not at fault.

"You will see there was very little done wrong at all," Gen. Lawson, the Chief of the Defence Staff, told reporters at a Kuwait air base that is home to the Canadian fighter jets that launch air strikes in Iraq and Syria. "In fact, the steps taken by the Canadian troops were perfect."

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He said the military is preparing recommendations on how to avoid a repeat of the tragedy, including taking into account how fatigue might affect interaction.

Sergeant Andrew Doiron was shot dead on the night of March 6 near the front lines in the battle with Islamic State fighters. He was killed by Kurdish peshmerga fighters who apparently thought approaching Canadian soldiers were enemy forces. Troops from Canada are advising the Kurds on military skills and tactics.

On Saturday, under heavy security – with aircraft providing cover overhead – Mr. Harper journeyed close to the front lines of the war with Islamic State while in northern Iraq, more than 40 kilometres west of Erbil and on the road to Mosul, now controlled by the jihadis. Gen. Lawson said the Prime Minister came within six kilometres of the front.

This also brought Mr. Harper close to the area where Sgt. Doiron was killed.

There have been a series of probes into the incident, including an investigation by Canada's special operations command, one by Canadian military police and another by American special forces commanders in Iraq. None has been made public so far – although Gen. Lawson, while saying he hasn't briefed the government yet, offered some key findings to media on Sunday.

"I think we will see that the fatigue of the soldiers who were up at the front, the peshmerga who were at the front, would have played a part," the Canadian commander said. "We're talking about battle fatigue."

Asked to explain what he meant, the general agreed that this meant the peshmerga on duty were fatigued from being under fire. "That's where the fatigue would come from – when you're up on the front line and you're on [duty] cycles that are very difficult to deal with."

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Gen. Lawson said he's got the Canadian military reports and a summary of the American probe. He predicted Ottawa would release portions of the Canadian reports – after some parts are censored – within the month.

Canada's deployment in the Middle East conflict includes Canadian fighter jets bombing Islamic State targets in Iraq and Syria, as well as nearly 70 special forces soldiers acting as military advisers to Kurdish fighters in the north.

The shooting of Sgt. Doiron created tension between the Canadians and their Kurdish allies. One peshmerga commander publicly blamed the Canadians, saying they didn't forewarn the Kurds they would be visiting a checkpoint near the front lines at night, and saying the soldiers from Canada spoke Arabic to them – leading the peshmerga to fear they were under attack from the enemy.

Gen. Lawson spoke following a speech by Mr. Harper at a Kuwait air base, where the Prime Minister thanked airmen and airwomen for their contribution to the fight against Islamic State militants who have wreaked havoc across Syria and Iraq. He said the Islamic State's chief goal isn't just to hold territory.

"It is to use that territory to launch a jihad, an orgy of terrorist violence, around the world … a war waged against everything we hold dear, freedom, democracy and human dignity, a war of enslavement and extermination, begun in Iraq and Syria, against anyone who is different than they are," Mr. Harper said.

His Saturday trip to near the front lines in the war with Islamic State militants produced something akin to a war zone photo-opportunity. The Prime Minister stood on a dirt berm using big high-tech binoculars that had been set up on a tripod for him to survey the progress in the battle against the jihadis. It was a gesture that might seem more suited for a military field commander than a civilian politician.

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The binoculars offered Mr. Harper a view of burning crop fields lit by the jihadis to obscure the landscape against coalition air strikes, as well as the territory the Kurdish peshmerga have recaptured since last fall when Canadian soldiers began advising them.

Canada and 60 other nations backing the U.S.-led fight against the militant group, which still controls one-third of Iraq, have laid out what they consider good reasons for joining the conflict.

It is also good politics – as far as the Conservatives are concerned. The surprise visit to Iraq, kept secret for security reasons until Mr. Harper arrived, reinforces a key message the nine-year-old Conservative government wants Canadians to remember as they head to the polls this fall. The hoped-for takeaway is that Mr. Harper is a strong leader making the tough decisions.

On Sunday, with a massive Canadian flag and two CF-18 fighters as a backdrop, the Prime Minister hammered this home again at the Kuwaiti air base.

He didn't mention NDP rival Tom Mulcair or Liberal opponent Justin Trudeau by name, but he nevertheless raised, and rejected, their criticism of his military deployment. The mission is expected to cost more than half-a-billion dollars by March, 2016.

Despite polls showing relatively strong public support for waging war against the Islamic State, Mr. Harper stands alone as the only major federal party leader to back the deployment of fighter jets to pound jihadi positions in Iraq and Syria.

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"Some will say we don't know how effective our actions will be, or whether this is the ideal strategy," the Prime Minister told Canadian Armed Forces personnel at the Kuwaiti air base. "Of course, how could we?" he said. "But what we do know, for certain, is this … in the face of this menace, the worst possible thing we could possibly do is nothing."

Also present when the Prime Minister journeyed near the front line Saturday was Farhang Afandi, an interpreter working on contract for the Canadian Armed Forces. He is the son of Hamid Afandi, a former Minister of Peshmerga Affairs and current commander of 10,000 men defending a section of the Kurdish front line outside Erbil.

Several weeks ago, Mr. Afandi blocked Globe and Mail reporter Mark MacKinnon from travelling to the area where Sgt. Doiron was killed, overruling permissions granted by the office of Kurdish President Masoud Barzani and the Ministry of Peshmerga Affairs.

The Department of National Defence has denied any role in turning back The Globe. On Saturday, Mr. Afandi, who was translating for the event, was in no mood to discuss what happened.

"I was just the messenger," he told The Globe of the decision to block Mr. MacKinnon.

Liberal defence critic Joyce Murray said she takes issue with how bits of information have been released over time regarding the incidents leading to Sgt. Doiron's death. "This slow leakage of interpretation is not adequate. The investigation should be made public," she said.

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Immigration Minister Chris Alexander rejected the suggestion the timing of the Prime Minister's trip was politically motivated. "I think anyone who argues that international terrorism has somehow been invented by any Western leader, any external leader, for their purposes is taking a very cynical view," he told CTV's Question Period.

NDP defence critic Jack Harris said it is "disturbing" the Prime Minister acknowledged in Kuwait that the government does not know whether the bombing campaign is effective or whether it is the right strategy. "I think that betrays a total lack of proper deliberation and consideration of the role that Canada should be playing in international affairs, particularly when it comes to life and death matters such as war," he said.

With a report from Bill Curry in Ottawa