Eight NATO troops and a contractor were killed when an Afghan pilot opened fire on Wednesday after a row at a Kabul training centre in one of the deadliest such attacks since the US-led invasion in 2001. The killings appeared to stem from an argument rather than terrorism, but served to highlight the prevailing insecurity in Afghanistan, 10 years after foreign troops ousted the Taliban from power. They were also likely to raise questions over a massive NATO-led effort to expand and train Afghanistan\'s military and police so they can take over when foreign combat operations are scheduled to end in 2014. The NATO-led training mission in Afghanistan confirmed that eight international troops and a contractor died in the shooting but did not reveal the nationality of the troops killed in line with policy. Afghan defence ministry spokesman Mohammad Zahir Azimi earlier gave further details of the clash, which is now over. \"At around 11:00am (0630 GMT) within the air force compound, an argument took place between an (Afghan) air force officer and foreign colleagues,\" he said. \"An exchange of fire followed. A number have been killed and injured.\" The Afghan pilot was shot dead by Afghan soldiers following the killings, which took place at a site shared by Kabul\'s military and civilian airports, he added. The Taliban claimed responsibility for the incident in a text message to AFP, although the militants are known routinely to exaggerate their claims. © AFPThere are around 130,000 international troops serving in Afghanistan But an Afghan official, speaking on condition of anonymity, identified the gunman as a 50-year-old pilot from a well-respected Kabul family, and said the shooting was the result of an argument and was not a terrorist act. The pilot is thought to have used a pistol in the shooting, the source added. The deaths are thought to represent the highest number of foreign forces killed in a single incident since September, when nine ISAF troops were killed in a helicopter crash in southern Afghanistan. It is also thought to be the deadliest incident for NATO troops at the hands of an Afghan dressed in military uniform. There is a history of Afghan forces attacking foreign soldiers who have been mentoring them ahead of limited foreign troop withdrawals due in July. NATO efforts to train and equip local forces so they can take responsibility for security across Afghanistan by 2014 have been hit by a string of attacks by militants who have apparently infiltrated the armed forces or who attacked while wearing unauthorised uniforms. Last November, six US troops were shot dead during a training session in eastern Afghanistan, apparently by a member of the Afghan border police. The defence ministry in Kabul was targeted last week by a gunman in army uniform wearing a suicide vest, in an attack that left three people dead. Earlier this month, another attack at a military base in the east killed nine including five foreign troops and four Afghan soldiers, while the police chief of Kandahar in southern Afghanistan was also assassinated. Monday\'s killings took place at NATO\'s Air Training Command Afghanistan centre, according to a spokesman for NATO\'s training mission in Afghanistan. The mission\'s commander, Lieutenant General William Caldwell, has called 2011 a \"pivotal\" year in which the total number of Afghan military and police should rise to over 300,000. The figure currently stands at over 180,000. He has said that the overall cost of the mission is some 40 billion dollars. There are around 130,000 international troops serving in Afghanistan, the bulk of them from the United States, although Afghan forces are in control of security in Kabul.