Marley Legers lost her husband Marc

A US F-16 dropped a 227-kilogram bomb on the men while they were taking part in a live-fire training exercise near Kandahar 10 days ago.

Another eight Canadian soldiers were injured, when the US pilot apparently thought his plane was under attack, and obtained permission from an air controller to return fire.

The US and Canadian militaries are investigating the incident, which was the result of "circumstances that defy understanding," said Mr Chretien.

Canada's army: More than the country deserves?

At least 12,000 people were at Edmonton's Skyreach Centre, usually a venue for ice hockey games, for the ceremony, which came at the end of more than a week of memorials across Canada.

The four dead men, all in their twenties, came from the Princess Patricia's Canadian Light Infantry, which is based near Edmonton.

"We have come together for comfort, to reaffirm the just cause for which they gave their lives," said Mr Chretien.

The US ambassador to Canada Paul Cellucci was also present at the ceremony.

Underfunding concern

Canada has 800 soldiers serving with the international forces in Afghanistan.

About 800 Canadian soldiers are in Afghanistan

On Sunday, a Canadian soldier from the same regiment was slightly wounded when his vehicle hit an anti-personal mine near Kandahar.

There were calls for Canada's military to pull out of the Afghan mission, after the "friendly fire" deaths.

The incident has led to a nationwide discussion of Canada's military, with claims that it is under-funded and poorly equipped.

"It is probably a better organisation than the people of Canada know or deserve," said Captain Jean-Marc Doucet, friend of one of the dead soldiers, at Sunday's ceremony.