KABUL, Afghanistan — An Afghan air force pilot opened fire on U.S. trainers at Kabul’s international airport Wednesday, killing nine in the deadliest attack on Americans inAfghanistan in nearly six years.

Details of what took place at North Kabul International Airport at about 11 a.m. were sparse.

The International Security Assistance Force, as the U.S.-led coalition is known, described the dead as “”eight ISAF service members and an ISAF civilian,”” but a Pentagonspokesman in Washington acknowledged that they were all Americans.

Marine Col. David Lapan said, however, that he could provide no details of what had happened. The ISAF said the dead had all been killed by small arms fire.

An Afghan Defense Ministry spokesman said the assailant was an Afghan pilot who opened fire on the trainers after an argument.

The Taliban took credit for the shootings, saying they took place while the trainers were meeting in a room at the headquarters of the Afghan Army Air Corps, which is on the grounds of Kabul’s airport.

In a statement posted on the Taliban website, spokesman Zabiullah Mujahid said the assailant died “”when he ran out of bullets.””

Not since a Taliban rocket blew a U.S. helicopter out of the sky in Kunar province on June 28, 2005, killing 16 U.S. soldiers, have so many Americans died as the result of a single assault.

Army Lt. Gen. William Caldwell, the commander of the NATO training mission in Afghanistan, called the attack a “”tragic loss.””

“”On behalf of … all of ISAF, I wish to convey our heartfelt condolences to the families of the trainers killed today,”” he said in a statement.

The shooting is certain to increase concern that Taliban sympathizers have infiltrated the Afghan security forces and that even the most secure locations are subject to attack. The North Kabul International Airport, which is home to NATO’s Air Training Command Afghanistan, is one of the most heavily guarded locations in the capital.

The attack came after a spate of assaults by Afghans dressed in uniform.

On April 16, a recent Afghan army recruit attacked a group of American soldiers with grenades at a forward operating base in eastern Afghanistan. Five U.S. soldiers were killed outright and a sixth died two days later in Germany, where he’d been taken for treatment. Four Afghans also were killed.

Last week, a Taliban sympathizer in an Afghan army uniform opened fire inside the Defense Ministry, killing two people. That shooting was timed to coincide with a visit by France’sdefense minister. Afghan officials said the sympathizer was wearing a vest packed with explosives but had been unable to detonate them before he was shot and killed.

Additionally, there have been at least four instances this year when Afghan soldiers opened fire on coalition troops. Wednesday’s incident, however, was the first such assault by a member of Afghanistan’s air force.

The attacks are part of what the Taliban have called their spring offensive, intended to take back ground they lost to the coalition after the Obama administration dispatched 30,000 additional troops to Afghanistan last year.

On Monday, nearly 500 prisoners, most of them captured Taliban fighters, escaped from a jail in the southern province of Kandahar through a tunnel that had been dug from a nearby house. The escape has raised fears that security will decline in Kandahar, a Taliban stronghold that’s been the focus of U.S. efforts to pacify the insurgency.

It was difficult to piece together what had happened Wednesday from the information that official sources released. Caldwell said Afghan President Hamid Karzai had ordered an investigation, and the ISAF said it was conducting its own probe.

Taliban militants said the “”suicide attacker”” opened fire on a meeting that included “”foreigners and Afghans”” in the heavily guarded air corps headquarters at the airport. Karzai said in a statement that five Afghans were wounded.

A Defense Ministry spokesman portrayed the attack as the result of an argument, though he revealed nothing about the cause of the disagreement.

“”Around 11 a.m., an Afghan army pilot opened fire after arguing with his foreign colleagues,”” Gen. Mohammad Zahir Azimi said. “”There was an exchange of fire, and a number were killed.””

Pan-Arab television network Al Jazeera quoted Azimi as saying the attacker had been in the air corps for 20 years. Other officials said he was from Tarakhil, a village near the airport, and that his brother was a doctor at Kabul’s military hospital. The brother couldn’t be reached for comment.