An Afghan soldier on Tuesday has killed two US trainers of the NATO-led foreign force and another Afghan soldier near the northern city of Mazar-e-Sharif.

Afghan and NATO forces were still investigating the circumstances around the incident, NATO said in a statement.

Earlier, provincial sources said an Afghan soldier had killed two members of the NATO-led force.

The incident occurred at a military training camp near to the northern city of Mazar-i-Sharif, the U.S. military said, adding the suspect was "thought to be an Afghan army trainer".

"A joint ... investigation is under way to determine the circumstances surrounding the shooting by an Afghan army soldier that led to the death and injury of several individuals," it said in a statement.

The incident comes on a day a major international conference met in Kabul.

The incident also comes a week after an Afghan soldier killed three British troops on a base in Helmand province in southern Afghanistan.

Agencies