WASHINGTON — A Pentagon investigation into the death of an American soldier in Afghanistan is looking at whether an Army brigade that is at the center of the Trump administration’s new war strategy had followed proper security procedures designed to protect United States troops from insider attacks by Afghan forces they train.
Cpl. Joseph Maciel, who was killed on July 7, was part of a group of soldiers assigned to protect American military advisers with the First Security Forces Assistance Brigade. He was with a team of roughly 25 trainers and soldiers that was attacked in Tarinkot, a town in the Taliban heartland, by what a local councilman described as an Afghan soldier who fired on the Americans.
The brigade’s roughly 1,000 soldiers are among the first conventional American forces since 2014 that are being sent into active fighting zones. They are spread across the country in small teams to help Afghan troops with training, intelligence and logistics.
Senior Pentagon officials, including Gen. Mark A. Milley, the Army chief of staff, and commanders at the American-led coalition’s headquarters in Kabul have declined to discuss details of the deadly shooting, which also wounded two American soldiers and an Afghan interpreter.
But two American military officers said the Pentagon was investigating whether the team in Tarinkot included enough security personnel to protect it from insider attacks. Since the shooting, American troops in the region have tightened security for units working alongside Afghan forces, according to a third military officer. All three spoke on the condition of anonymity to discuss the investigation.
More than 2,200 American forces have died in Afghanistan since 2001. But American officials are sensitive about Corporal Maciel’s death, given the high profile of the advisory brigade, which is on its first deployment and is a central part of the Trump administration’s strategy to exit the war by escalating training of Afghan troops.
In June, the advisory brigade’s commander, Col. Scott Jackson, said senior Afghan forces had pledged to protect the American trainers. “On Day 1, they uniformly said the most important thing to them is the safety of their advisers,” Colonel Jackson told reporters.
The team in Tarinkot had been looking for new housing quarters to replace destroyed barracks where American, Dutch and Australian troops had been stationed years earlier.
Abdul Karim Khadimzai, a local councilman from the surrounding Oruzgan Province, said it was not clear why the Afghan soldier fired at the American troops. The Afghan soldier was taken into custody, and several others were also arrested, according to a military document obtained by The New York Times.
In a statement, a Taliban spokesman, Qari Yosuf Ahmadi, said that the assailant had acted alone — but that the militant group appreciated the killing.
Corporal Maciel, from South Gate, Calif., was assigned to the First Battalion, 28th Infantry Regiment, which is protecting the advisory brigade with so-called Guardian Angel soldiers to safeguard against insider attacks.
The attacks on American troops by allied Afghan soldiers are a grim feature of the war, and highlight cultural tensions between the partnered forces.
In some cases, investigations have found, the Taliban ordered the attacks, which peaked in 2012 and accounted for 15 percent of coalition troops who were killed or wounded in Afghanistan that year. Coalition forces were targeted in four insider attacks last year, including one that killed three United States soldiers in eastern Afghanistan.
The surge prompted the creation of the Guardian Angel program, which is designed to ensure that American military advisers working with Afghan troops are more fully protected from insider attacks. Soldiers assigned to Guardian Angel duties receive special training, carry loaded weapons and wear body armor and helmets whenever American advisers are working with Afghans — even when inside secure bases.
As they have moved closer to the front lines, American troops in the southern city of Kandahar and in Oruzgan, Zabul and Daikundi Provinces work under stricter security guidelines when training Afghan soldiers. In some areas, Army troops are required to assign at least one Guardian Angel soldier to each military adviser; in others, several Guardian Angel soldiers might protect a small group of American forces that are working with a larger number of Afghans.
According to two additional American military officers, the team in Tarinkot was using more relaxed security protocols. More Afghans than were expected showed up for the July 7 mission, outnumbering the Americans and making security more difficult, according to one of the officers.
Another one of the officers, who has worked with the advisory brigade, cited intelligence that was shared among American units in southern Afghanistan weeks earlier and that indicated that the Taliban were planning an insider attack at a small base near Kandahar, where the team was based. But the intelligence reports did not mention Tarinkot.
In recent months, the advisory brigade had stepped up its security measures to ward off insider attacks and to ensure that the Afghan soldiers were properly screened before working alongside American troops, the officer said.
Some of those measures included seizing and searching the cellphones of Afghan soldiers for any connections to the Taliban, the officer said. He said the Afghan soldiers who were training in Tarinkot then started bringing backup phones and concealing them from the American advisers.
Even before the July 7 attack, two Defense Department officials said, the brigade was struggling to find its footing — not just because its soldiers had recently arrived, but also because of its new role in areas of Afghanistan that American forces had not been in years.
Once they settled in, which took months, the advisers worked with little guidance and little understanding of the Afghan forces they were supposed to be training, said the Defense Department officials, who also spoke on the condition of anonymity.
Jason Dempsey, an adjunct senior fellow at the Center for a New American Security, said it was unlikely the advisory brigade would have a lasting influence.
“They’re probably just figuring out who’s in the zoo just a few months before they have to leave, and then the next group will have to do this all over again,” Mr. Dempsey said.
But the next group is not expected to arrive in Afghanistan until three months after Colonel Jackson’s brigade leaves this fall, one of the military officials said. That means many Afghan troops will go without American training until then.
Taimoor Shah contributed reporting from Kandahar, Afghanistan.