A joint US-Canadian inquiry has blamed two F-16 fighter pilots for killing four Canadian soldiers in a so-called "friendly fire" incident in Afghanistan.

US Marine Corps Lieutenant-General Michael DeLong, deputy commander of US Central Command, told a news conference in Florida that the pilots had failed to exercise appropriate flight discipline.

The two American pilots... were the direct cause of the incident

John McCallum, Canadian defence minister

Lieutenant-General DeLong said the Air Force will consider taking disciplinary action against the men.

A separate Canadian inquiry into the incident reached the same conclusion.

The mistaken attack was the worst case of friendly fire of the nine-month war in Afghanistan.

Mistaken identity

The Canadian troops were on a night-time training exercise near the southern Afghan city of Kandahar when they came under attack by the F-16s.

More than 800 Canadian troops are serving in Afghanistan

The two fighter planes were returning from a mission over Afghanistan when they saw what they believed to be enemy fire.

Lieutenant-General DeLong said the lead pilot reported hostile activity and the second pilot requested permission to fire.

He was told by American air controllers to wait for verification, but the pilot decided to act in self-defence and dropped a 500-pound (227 kg) laser-guided bomb onto his target, killing the Canadian soldiers.

Lieutenant-General DeLong said this amounted to "inappropriate use of lethal force".

He said failings in the pilots' "immediate command structure" also contributed to the accident.

Canadian anger

According to the separate Canadian inquiry, Canadian troops had notified American military officials that they would be conducting live-fire exercises that night.

Retired Canadian general Maurice Maril, who led the investigation, said the pilots' actions "represented a failure of airmanship and technique for the wingman and a failure of leadership for the flight leader".

Canadian Defence Minister John McCallum said the pilots "contravened established procedures and were the direct cause of the incident".

The incident caused outrage in Canada.

It was the first time Canadian troops had been killed in a combat zone since the Korean War in the early 1950s.

Earlier this month, a US military investigation recommended the pilots, identified as Major Harry Schmidt and Major William Umbach, face a hearing that could lead to criminal charges against them.