WASHINGTON?The pilot of an American F-16 bombed Canadian soldiers in Afghanistan believing they were enemy forces firing on him, defense officials said Thursday. Four Canadians were killed and eight wounded.

The soldiers were the first Canadians killed in a combat zone since serving alongside Americans in the Vietnam War. Their unit, the 3rd Battalion of the Princess Patricia’s Canadian Light Infantry, based near Edmonton, Alberta, was the first all-Canadian unit to suffer fatalities in a half century.

Without getting permission, the U.S. Air National Guard fighter dropped a 500-pound laser-guided bomb on troops participating in a nighttime live-fire training exercise near the southern Afghanistan city of Kandahar.

The jet, flying in tandem with another American F-16, had been sent out on patrol. It was unclear whether they had been given any other mission.

It appeared the pilots did not know they were flying over an area restricted for training?and so fire from the training exercise made them believe they were under attack, officials at the Pentagon said.

One sought permission to bomb and was given the go ahead only to mark the target, a senior Pentagon official said. On a second fly-around, again thinking he was under fire, he dropped the bomb in what he thought was a self-defense move, officials said.

Canadian Defense Minister Art Eggleton, who called the deaths shocking, said Thursday that one of the injured had life threatening wounds and the other seven were in stable condition.

U.S. and Canadian officials said the accident occurred at 1:55 a.m. local time Thursday (5:25 p.m. EDT Wednesday) about 10 miles south of Kandahar, a former Taliban stronghold. The two countries plan a joint investigation.

“As to the circumstances of what appears to have been a terrible accident, clearly there are many questions that the families, and all Canadians, expect to have answered,” Canadian Prime Minister Jean Chretien said in a statement.

After daylight in Kandahar, clusters of Canadian soldiers gathered at a bulletin board to read a posted statement about the deaths and injuries. Around the base, troops talked quietly in small groups.

Chretien said President Bush had called to offer his condolences.

Canada’s defense chief, Lt. Gen. Ray Henault, told reporters in Ottawa that the area was recognized as a training area and the aircraft were using very strictly controlled routes.

“How this can happen is a mystery to us. Without a doubt, there was a misidentification,” Henault said.

At the coalition base in Kandahar, U.S. Army Col. Frank Wiercinski called the Canadians an integral part of the coalition’s operations in Afghanistan.

“They are our comrades-in arms,” Wiercinski said, standing in front of a Canadian flag at half staff. “In the last several months, we have lived together, we have fought together and now we will mourn together.”

Canadian Army Lt. Col. Pat Stogran, the battalion commander, pledged to friends and families that the wounded would receive the “best possible support,” and that the battle group would remain steadfast.

“These young men were among the finest, bravest paratroops I have ever soldiered with,” Stogran said. “They will not be forgotten.”

Officials said the site of the accident was a former al Qaeda training camp now used daily by coalition forces for live-fire exercises.

Canadian forces are fighting alongside U.S. and European troops seeking to hunt down remnants of Osama bin Laden’s terrorist organization and holdouts from Afghanistan’s former ruling Taliban militia.