Updated April 27, 11:40 a.m. EDT

KAISERSLAUTERN, Germany — In what officials term the deadliest such incident to date, eight U.S. servicemembers and an American contractor working for the International Security Assistance Force were gunned down by an Afghan pilot at Kabul airport early Wednesday.

A senior defense official confirmed to The Associated Press that all the victims were American, but could not say what branch of service the military members were. ISAF Joint Command released statements throughout the day confirming the incident, but would go no further, pending family notifications.

A spokesman for the NATO command overseeing the training of Afghan forces, U.S. Air Force Lt. Col. David Simons, confirmed that the shooting involved its troops at a compound used to train the Afghan air force.

Col. Baha Dur, chief of public relations for the Afghan National Army at Kabul military airport, had told CNN earlier in the day that the gunman “opened fire at armed U.S. military soldiers inside the airport after an argument between them turned serious.”

Simons declined to describe how the shooting started.

“There was an incident that led to violence,” he said.

First reports of the incident came in at 10:25 a.m., according to ISAF. A quick reaction force of Afghan and coalition troops responded to the shooting, which happened in a secure area of the airport in the capital. The compound is within sight of the headquarters of the ISAF Joint Command, which oversees the war’s day-to-day operations.

A Stars and Stripes review of data earlier this month, before Wednesday’s incident, showed that some 13 troops with the International Security Assistance Force had been killed this year when Afghan police, soldiers or security guards — or insurgents who infiltrated their ranks — attacked coalition forces. These types of killings have accounted for the deaths of at least 38 coalition personnel since 2009.

The killers, it was determined, are not usually Taliban sleeper agents or impostors. They often appear to be regular Afghan troops who start shooting after some dispute with coalition troops, according to the NATO command in charge of training Afghan security forces.

“[The shootings are] usually related to people getting into arguments,” Simons said in mid-April, citing incident reports.

“Let’s put it in the vernacular of a bar fight. But here, they have weapons,” Simons said.

Afghanistan Defense Ministry spokesman Gen. Mohammad Zahir Azimi told The Associated Press that the shooter was a military pilot of 20 years.

An Afghan pilot who spoke to AP on condition of anonymity said the gunman was Ahmad Gul, a 50-year-old pilot from Kabul province.

In a statement to AP, Taliban spokesman Zabiullah Mujahid claimed the gunman was impersonating an army officer and that others at the facility helped him gain access. The gunman killed nine foreigners and five Afghan soldiers, he said. The Taliban often exaggerate the number of casualties caused by their attacks.

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