Gen. Mohammad Zahir Azimi, a spokesman for Afghanistan's Defense Ministry, said a "terrorist in an army uniform" opened fire on both local and international troops. Azimi said the shooter had been killed and that three Afghan army officers were wounded. He did not offer a motive for the assault.
U.S. officials identified the dead U.S. officer as a major general. One U.S. official said about half of the wounded were Americans. That officials spoke on condition of anonymity as the officials were not allowed discuss the information by name ahead of an official announcement.
Germany's military said 15 NATO soldiers were wounded in an assault launched "probably by internal attackers." The wounded included a German brigadier general, who the German military said was receiving medical treatment and was "not in a life-threatening condition."
NATO said it was investigating the attack, which Afghan President Hamid Karzai condemned as "cowardly."
It is "an act by the enemies who don't want to see Afghanistan have strong institutions," Karzai said in a statement.
In a statement sent to journalists, Taliban spokesman Zabihullah Mujahid praised the "Afghan soldier" who carried out the attack, as well as a police officer in Paktia province who shot at NATO forces earlier Tuesday. He did not claim the attacks.
Qargha is known as "Sandhurst in the Sand"— referring to the famed British military academy — as British forces oversaw building the officer school and its training program. In a statement, the British Defense Ministry said it was investigating the incident and that "it would be inappropriate to comment further at this time."
Soldiers were tense in the immediate aftermath of the shooting. One soldier in a NATO convoy leaving Camp Qargha fired an apparent warning shot in the vicinity of Associated Press journalists who were in a car, as well as pedestrians standing nearby. AP photographer Massoud Hossaini said he and an AP colleague were about 15 feet (5.5 meters) from the soldier at the time. Hossaini said he thought the soldier fired a pistol.
"The vehicle before the last one, someone shouted at me," Hossaini said. "The last one, the soldier opened fire."
No one was wounded.
The Qargha shooting comes as so-called "insider attacks" — incidents in which Afghan security turn on their NATO partners — largely dropped last year. In 2013, there were 16 deaths in 10 separate attacks. In 2012, such attacks killed 53 coalition troops in 38 separate attacks.
Such "insider attacks" are sometimes claimed by the Taliban insurgency as proof of their infiltration. Others are attributed to personal disputes or resentment by Afghans who have soured on the continued international presence in their country more than a dozen years after the fall of the Taliban's ultra-conservative Islamic regime.
Foreign aid workers, contractors, journalists and other civilians in Afghanistan are increasingly becoming targets of violence as the U.S.-led military coalition continues a withdrawal to be complete by the end of the year.
In eastern Paktia province, an Afghan police guard also exchanged fire Tuesday with NATO troops near the governor's office, provincial police chief Gen. Zelmia Oryakhail said. The guard was killed in the gunfight, he said. It wasn't clear if the two incidents were linked and police said they were investigating the incident.
Meanwhile Tuesday, a NATO helicopter strike targeting missile-launching Taliban militants killed four civilians in western Afghanistan, an Afghan official said Tuesday. NATO said they were investigating the attack.
The attack in western Herat province comes as civilian casualties from NATO attacks remain a contentious issue across the country. Almost 200 people protested against NATO in Herat on Tuesday, carrying the bodies of the dead civilians into the provincial capital and demanding an investigation.