An Afghan ex-pilot gunned down eight US troops and an American contractor yesterday after an argument flared at a Kabul training centre, the worst attack of its kind in almost a decade of war.

Although the killings appear to have stemmed from a disagreement rather than a rebel attack, they highlighted the prevailing insecurity in Afghanistan, 10 years after a US-led invasion ousted the Taliban from power.

The deaths are also likely to raise fresh questions over the massive Nato-led effort to expand and train Afghanistan’s military and police, so they can take control of security when foreign combat operations end in 2014.