KABUL — An Afghan pilot opened fire and killed six foreign troops Wednesday after a row at a NATO training centre for the national air force in Kabul in one of the deadliest such clashes yet, officials said.

A spokesman for the NATO-led International Security Assistance Force (ISAF) confirmed the deaths and that shots had been fired at the facility, part of the Kabul airport complex.

"Six International Security Assistance Force service members died following a shooting incident here today," an ISAF statement said, without identifying their nationality in line with policy.

Afghan defence ministry spokesman Mohammad Zahir Azimi earlier confirmed the clash and said there were casualties.

"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 Taliban claimed responsibility for the incident in a text message to AFP, although the militants are known routinely to exaggerate their claims.

"A suicide fighter who had a job there carried out an armed attack resulting in massive Afghan and foreign casualties," spokesman Zabihullah Mujahed said.

But an Afghan official source, speaking on condition of anonymity, said the gunman was a 50-year-old pilot from a well-respected Kabul family, and that the shooting was the result of an argument and was not a terrorist act.

The incident took place at NATO's Air Training Command Afghanistan facility, according to a spokesman for NATO's Afghanistan training mission said.

An AFP reporter at the scene heard sirens and reported a heavy presence of Afghan soldiers. The incident has now concluded.

NATO efforts to train and equip local forces into taking over responsibility for security across Afghanistan by 2014 have been hit by a string of attacks carried out by militants who have apparently infiltrated the armed forces or who committed attacks wearing unauthorised uniforms.

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.

There is also a history of Afghan forces opening fire on foreign forces who have been mentoring them.

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.

Limited foreign troop withdrawals are due to begin in July ahead of a complete pull-out of international combat troops in 2014.