Canadian and U.S. military officials are reviewing whether friendly fire played a role in any deaths or injuries during a firefight with the Taliban.

Pte. Robert Costall, a machine-gunner, and a U.S. soldier -- national guardsman Sgt. 1st Class John Stone, 52, a medic -- died in that encounter last Wednesday. Five other soldiers were wounded, including three Canadians.

"'The initial findings justify the requirement for further investigation to determine the facts and circumstances surrounding the firefight, including whether any of the casualties resulted from friendly fire'," said CTV's Ellen Pinchuk from Kandahar early Tuesday, reading from a National Defence news release.

"It is inappropriate for us to speculate on the events of 28 March, as they will be examined as part of the investigations," the release said.

However, the release went on to say: "Coalition military operations in Afghanistan are complex.

"Terrain, weather and threat levels combine to create an extremely challenging operating environment. The fact the incident occurred at night, with attacks from multiple directions, just adds to the complexity."

There is no indication of how long the investigation will take. The Canadians and Americans will each do separate investigations.

The incident occurred in Sangin district of Helmand province, about 110 km north of Kandahar.

Afghan National Army troops first engaged Taliban insurgents.

A quick reaction force -- 7 Platoon of Charlie Company of the Princess Patricia's Canadian Light Infantry -- was dispatched by helicopter to reinforce the Afghan troops.

Pinchuk had video of the remote forward operating base, which is essentially a dusty plain, with the base's boundaries marked with concertina wire and a slight berm.

"The attack came at night from several sides by the Taliban," Pinchuk said. "It's possible that in the crossfire, somebody could have shot at one of their own."

While military aircraft, including B-52 bombers, were used during the lengthy battle, Pinchuk said an errant air strike isn't suspected.

"We're told that it could have been Canadian, U.S. or Afghan National Army fire, or it may have been enemy fire from the Taliban. We'll have to wait and see what the results of the investigation turn up," she said.

Costall's body arrived in Canada on Saturday, where his devastated wife Chrissy and Costall's parents met his coffin.

His body was taken to Toronto for a routine autopsy.

That same day in Afghanistan, Canadian troops were dispatched to the same area he died as part of Operation Ketara, a Pashtu word for dagger.

Helmand province is a hotbed of not only the Taliban, but opium growers too.

Part of the mission's purpose is to secure the area so that local Afghan authorities can plow the fields under.

Gen. Lewis McKenzie comments

Maj.-Gen. Lewis McKenzie (ret.) told CTV Newsnet the following about what might have happened during the battle: "You're not just firing out like covered wagons in a defensive position. You have people mixed in and around you.

"Unfortunately, when that happens, friendly fire incidents are terribly easy to explain and must be accepted," he said.

Clues that investigators will look for will include things like the calibre of any bullets recovered, McKenzie said, although he noted the Afghan National Army uses AK-47 assault rifles, as do the Taliban insurgents.

Soldiers involved in the firefight will be interrogated, he said.

"They try and recreate this thing," he said. For example, investigators might learn that Canadian soldiers were shooting at a group of insurgents, but some of their comrades wound up somewhere behind the insurgents.

McKenzie said people should remember that whatever the outcome of the friendly fire investigation, Canadian, U.S. and Afghan troops did repel the Taliban and caused significant enemy casualties.

"In my estimation, it's a combat casualty -- full stop."

Friendly fire in Afghanistan has been in the news before.

In April 2002, four Canadian soldiers died near Kandahar when a U.S. fighter jet bombed them during a night training exercise.

The "hype" surrounding that incident had him wondering how the general public would receive news of another possible friendly fire incident, McKenzie said.

With a report from CTV's Ellen Pinchuk