Fifty investigators are examining a fire at a Canadian military base.

The fire killed four soldiers and injured 39 others, Prime Minister Mark Carney said Monday.

People are asking why training continued when officials knew a fire was burning nearby.

Carney told Parliament in Ottawa that the Canadian Forces National Investigation Service is leading the investigation.

The Royal Canadian Mounted Police is helping.

The fire happened Saturday at Canadian Forces Base Wainwright in Alberta.

Carney said a fire was burning in the training area.

Strong winds pushed it nearly a kilometer in less than a minute toward gathered soldiers.

He said investigators have not found what started the grass fire.

He later told reporters that the government would get answers as quickly and openly as needed.

The fire caught soldiers from the 3rd Battalion, Princess Patricia's Canadian Light Infantry.

Army reservists doing live-fire training were also caught.

Nineteen of the injured were in critical condition as of Monday.

Opposition leader Pierre Poilievre represents Wainwright in Parliament.

He said many suffered severe burns and need weeks or months of intensive care.

Maj. Gen. Wade Rutland said Sunday that officials knew about the fire for hours.

But they believed it was contained, so training continued before winds suddenly changed.

About 84 soldiers from Charlie Company were training at two locations.

The fire swept into the second area.

Carney said the soldiers were preparing for a mission next spring.

They would reinforce Canadian troops with NATO in Latvia.

The military named the dead.

They are Sgt. Morgan Wong of Edmonton and Pvt. Shaun Farrell of Prince Albert, Saskatchewan.

They also include Pvt. Aidan Goulding of North Vancouver, British Columbia, and Pvt. Hayden Lykkemark of Langley, British Columbia.

Carney ordered flags lowered to half-staff on all federal buildings nationwide on Sunday.

Military liaison officers are helping families at hospitals in Edmonton, Calgary, Red Deer and Wainwright.

Mental health teams and chaplains are supporting soldiers and their families.