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KABUL, June 20 (Reuters) - Three Canadian soldiers died in southern Afghanistan on Wednesday when a roadside bomb blew up beside their small unarmored vehicle in what was meant to be a secure zone, a senior military official said.

Brigadier-General Tim Grant said the soldiers had been conducting a resupply operation on a short narrow road between two checkpoints in the Panjwai district, about 25 miles (40 km) west of Kandahar.

"We look at this as an unfortunate accident. The vehicle was appropriate to the task at hand and the terrain they were traveling in," he told reporters in Kandahar, the southern city where Canada has a 2,500-strong mission.

Grant's remarks were shown live on Canadian television. Canada has now lost 60 soldiers since sending troops to Afghanistan in 2002 as part of the U.S.-led war on terror.

Grant said the road between the checkpoints led past high mud walls and through grapefields, and described the terrain as very difficult to operate in.

"A determined enemy clearly was able to penetrate the defenses and the observation in the area to plant the device," he said.

The Taliban claimed responsibility for the blast, which a spokesman for the insurgents said was in Helmand province. They had earlier claimed 10 NATO soldiers had died in a roadside blast, but frequently inflate their successes.

In a separate incident, a roadside bomb killed a district police chief in southeastern Khost province. The Taliban claimed responsibility for that blast too.

Violence has surged in Afghanistan in recent months after a traditional winter lull, with foreign forces launching attacks against Taliban strongholds in the south and east and the guerrillas hitting back with roadside and suicide bombings.

The latest NATO deaths bring to 606 the number of foreign troops killed in action in Afghanistan since the overthrow of the Taliban in 2001 after the Sept. 11 attacks on the United States. Some 55 foreign soldiers have been killed in fighting so far this year.

More than 4,000 people were killed in fighting in 2006, a quarter of them civilians and about 170 of them foreign soldiers.

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