Two children died Sunday after Canadian troops opened fire on a car they feared was about to attack their convoy in Afghanistan, the military said Monday.

A gunner in a light-armoured vehicle pulled the trigger on a 25-millimetre cannon after the driver of a car ignored repeated signals to keep a safe distance, officials said.

The incident occurred around sunset Sunday, when the car approached within 10 metres of the convoy, a Canadian military statement said.

Witnesses reported the four-year-old girl was struck in the head and her two-year-old brother in the chest.

The children's grief-stricken mother was seen pacing the hallway at the local hospital, sobbing and shrieking that they were killed by foreigners for no reason. The father was treated for lacerations.

"These are very tragic circumstances," Defence Minister Peter MacKay said Monday in Ottawa. "Having said that, the soldiers are living, breathing and operating in very tough, trying and intense circumstances."

At least 12 Canadians have been killed by suicide bombings carried out by the Taliban, he said.

"With that as a backdrop, when these tough circumstances arise, we always take the important time to investigate what took place," he said. "There are rules of engagement followed by Canadian soldiers .… In each circumstance where this type of unfortunate tragedy occurs, soldiers have been found to have followed these rules of engagement."

Must take direct action

Expressing regret, the Canadian military said in an earlier statement, "Our thoughts are with the families and friends of the deceased during this difficult time."

"Our soldiers are trained to take all appropriate steps to minimize civilian casualties. However, they must take action to protect themselves when they believe they are being threatened."

The military is trying to reach the children's family to express its condolences, Capt. Sonia Dumouchel-Connock said Monday in Kandahar. She declined to say whether the family would be compensated financially.

The military statement said there were two other occupants in the vehicle who were not injured.

Afghan police and coalition forces will be investigating Sunday's incident. Dumouchel-Connock declined to say whether a bomb was in the vehicle, only that there's an ongoing investigation.

Coalition forces will continue to run frequent public service announcements and advertising campaigns to warn locals to keep a safe distance from convoys and many locals are scared of getting close to military vehicles.

NATO commanders say they take all reasonable precautions and that militants, who regularly use civilian cars loaded with explosives in suicide missions, are to blame for endangering innocents.

Human Rights Watch estimates at least 300 Afghan civilians were mistakenly killed by coalition forces in 2007, with thousands dead since the mission's start six years ago.

Afghan and United Nations officials have urged international troops to take extra precautions to prevent civilian casualties.

With files from the Associated Press