From this morning's WSJ:

KABUL—An Afghan soldier killed two American service members and wounded six other U.S. military personnel in eastern Afghanistan on Saturday, U.S. and Afghan officials said.

The incident occurred in Nangarhar province, an area where U.S. and Afghan forces have been fighting both Taliban and Islamic State fighters. Nangarhar is considered one of the more dangerous areas in the country.

“Current reports indicate an individual in an Afghan army uniform opened fire on the combined U.S. and Afghan force with a machine gun,” said Col. Sonny Leggett, a spokesman for the U.S. command in Afghanistan early Sunday.

Ajmal Omar, deputy chief of the Nangarhar provincial council, said both American and Afghan forces were visiting an army base in Sherzad district on Saturday afternoon when an Afghan soldier opened fire on American troops. American soldiers then killed the shooter, he added.

Another member of the provincial council, Obaidullah Shinwari, said the attack was caused by a verbal argument between the two sides.

Six injured U.S. service members are receiving medical treatment at a U.S. facility, Col. Leggett said in a statement Sunday. He added that the incident is under investigation and “the cause or motive behind the attack is unknown at this time.”

In accordance with Pentagon policy, the service members killed in the incident weren’t identified.

More than 2,400 troops have been killed in Afghanistan since the war began in 2001.

Saturday’s attack comes as the Trump administration struggles to determine the way forward in the war, now in its 18th year. Mr. Trump has sought to end so-called endless wars, including in Afghanistan, but the Pentagon still maintains about 13,000 troops there.

Officials have worked toward a peace agreement between the U.S. and the Taliban, but the path remains elusive and such talks, which restarted in December, haven’t made substantive progress, officials said.

Regardless of the outcome of that process, Mr. Trump has vowed to reduce the number of American forces in Afghanistan, and officials have said the initial reduction could bring home as many as 4,000 troops, leaving a total of about 8,600 troops on the ground there.