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OTTAWA, July 4 (Reuters) - The six NATO soldiers killed by a roadside bomb in Afghanistan on Wednesday were Canadian, a senior military official said.

The six men and a local Afghan interpreter died when their armored vehicle hit the device about 20 km (13 miles) southwest of the southern city of Kandahar, which is home to Canada's 2,600-strong mission.

It was the single deadliest attack involving Canadian troops in Afghanistan since six soldiers were killed by a roadside bomb in early April. So far 66 have died since Ottawa sent troops to Afghanistan in 2002 to help fight Taliban militants.

"Clearly, they have managed to kill six great young Canadians today which is an absolute tragedy," Brigadier-General Tim Grant told a televised news conference in Kandahar.

The blast occurred as the troops were returning in a convoy of 12 vehicles from a joint operation with the Afghan national army.

"As with every attack we will look at what has happened and will decide at that time if there is something we need to do to increase the protection for our soldiers," said Grant.

The deaths will only increase doubts among Canadians about the wisdom of the mission, which is due to end in February 2009. Critics say it is focused too much on fighting and not on rebuilding the country.

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