On Tuesday, a soldier in the Afghan army opened fire on a group of high-ranking NATO coalition members, killing an American major general. The attack, which occurred at the British-run Marshall Fahim National Defense University outside of Kabul, comes amidst an increase in violence in Afghanistan over the past year.

The slain American two-star Major General, Harold Greene, is the highest-ranking US military officer to have been killed in hostilities since the Vietnam War. General Greene was a veteran acquisitions officer who was assigned in January to create a plan for the Afghan military to better manage its soldiers and weaponry.

According to the German military, 15 NATO troops were also wounded in the attack, including a German brigadier general, two Afghan generals and an Afghan officer. Approximately half of the wounded were Americans and several were British. The Afghan soldier responsible for the attack was killed during the fighting.

The attack took place around noon local time. The insider, wielding an American-issued M16, emptied an entire magazine of his semiautomatic weapon from a guard post before being killed.

This was the first insider attack in the Afghan army in several months. In 2012, 53 members of the NATO coalition were killed in 38 different attacks perpetrated by members of the Afghan army. Due to protective measures—specifically, the physical separation of NATO troops from the Afghan army and giving NATO troops special guards—casualties fell sharply in 2013. In that year, 16 NATO troops were killed in 10 “green-on-blue” incidents. However, while killings of NATO troops by Afghan security forces dropped, instances of Afghan soldiers killing others in the force increased.

The Marshall Fahim National Defense University is situated on a military camp west of Kabul. Among those injured in the attack was the Afghan general overseeing the university.

The British-Afghan academy is a part of a larger effort by NATO forces to train the 350,000-strong Afghan army in preparation for the removal of two-thirds of the United States’ combat troops. According to the BBC, the academy’s first class is expected to graduate at the end of next month.

The BBC stated that the killing was “hugely embarrassing” for the British, who run the academy, “as well as the Americans who are building a major military training facility just alongside it.” The BBC described the American complex as “huge” and noted that some Afghans are calling it their “National Defense University.” The news agency continued, “It will ask searching questions, this kind of incident, to donors in the West as to whether it is worth continuing with the efforts that they are making to train the Afghan army.”

At a press conference Tuesday evening, Pentagon press secretary Rear Admiral John Kirby described the “insider threat” as a “pernicious threat.” He told the press that the threat was “difficult to always ascertain—to come to grips with the scope of it, anywhere you are, particularly in a place like Afghanistan.”

“And, Afghanistan is still a war zone, so it’s impossible to eliminate, completely eliminate, that threat, particularly in a place like Afghanistan.”

According to the UN, in the first six months of 2014, 1,564 civilians died as a result of fighting in Afghanistan. This is a 17 percent increase compared to the first six months of 2013, during which 1,342 civilians died.

On Tuesday, the same day as the military academy incident, a NATO helicopter fired on a vehicle in western Afghanistan filled with civilians. The attack killed four civilians returning from a wedding ceremony.

Also on Tuesday, an Afghan police guard opened fire on NATO troops in the eastern Paktia province. The NATO troops returned fire, killing the guard. At this point, there is no evidence to suggest that this incident and the shooting at the military academy are linked.

After the shooting at the military academy, a NATO solider leaving the academy fired a warning shot at two Associated Press reporters who were first to the scene.