Canada deploys 50 investigators to army base where a grass fire raced a kilometre in 30 seconds, killing four soldiers

The blaze broke out at around 4pm on Saturday at Canadian Forces Base Wainwright in Alberta, leaving 39 people injured. Prime Minister Mark Carney says the cause remains unknown. Major General Wade Rutland has dismissed any suggestion of outside interference. Parliament observed a moment of silence for the dead on Monday.

The incident ranks among the worst peacetime tragedies the Canadian military has suffered on domestic soil.

Carney has promised a 'thorough and rapid' investigation into the disaster.

Viral footage of a fireball at the base actually showed an Italian arms factory blast in August.