Sri Lanka's top diplomat in Canada has dismissed claims her government committed war crimes as it crushed the Tamil Tigers' separatist insurgency last year, and says the world has no business investigating such "unsubstantiated" allegations in a sovereign country.

"We say that there were no war crimes," Chitranganee Wagiswara, the Sri Lankan High Commissioner in Ottawa, told The Globe and Mail. "We have been handling this conflict, so let us handle this."

International attention turned this week to alleged atrocities by both sides during Sri Lanka's push to end the Tigers' 26-year militancy during the first five months of 2009. The claims were detailed in a report released Monday by the International Crisis Group, a respected conflict-prevention body led by Canadian jurist Louise Arbour, a former international war-crimes prosecutor.

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The Brussels-based group said its eight-month investigation found "credible evidence" that Sri Lankan forces deliberately shelled civilians, hospitals and humanitarian operations, and that the Tigers forcibly kept Tamils inside the conflict zone and shot many who tried to flee to government-held areas.

Ms. Arbour urged Canada, among other countries, to press for a United Nations investigation and to probe and prosecute alleged war criminals domestically under the universal jurisdiction of its war crimes laws. Canada has a large Sri Lankan population and its estimated 200,000 Tamils are said to be the largest such group outside Asia.

"We totally reject these allegations in the [crisis group]report," said Ms. Wagiswara, who attributed the claims to Tiger leaders and their supporters abroad in an attempt "to discredit the government" as it tries to move on from the war, and engage with the world on economic and social issues.

The diplomat said any concerns about the war will be examined in Sri Lanka by a commission newly appointed by President Mahinda Rajapaksa.

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The crisis group report, however, said an impartial domestic investigation is impossible "given the entrenched culture of impunity" in Sri Lanka, which expelled foreign journalists and aid workers during the war's final months. That impunity, Ms. Arbour said in an interview, was bolstered by an international community eager to see the end of the ruthless Tiger movement and happy to look the other way "to give [the Sri Lankan government]a chance to finish it off for good" last May.

"Conveniently, these governments allowed themselves to believe the Sri Lankan narrative, which is that they did it successfully at very low cost," Ms. Arbour said, adding that her report found "that it was done at a terrible cost."

In addition to as many as 40,000 civilian lives, the cost includes the emboldening of other countries to employ what she called "the Sri Lankan option" of counterinsurgency: "Don't be too fussy about the distinctions between combatants and civilians, keep the world at bay and go for it as rapidly and as brutally as you can," she said.

An impartial outside probe of Tiger atrocities is just as crucial, Ms. Arbour said, because a Sri Lankan investigation would be too easy for Tamils to dismiss "as victor's justice or government propaganda," and as fuel to revive the militant movement.

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If there were no war crimes, "why don't they agree to an international investigation?" Ms. Arbour said. "Is everybody wrong except them?"

Editor's Note: This online article has been changed to include a clarification to the secondary headline in the original online version.