Three U.S. soldiers killed, one wounded by Afghan soldier - officials | Reuters:
The shooting occurred in the Achin district of Nangarhar province, where U.S. special forces have been fighting alongside Afghan troops against Islamic State and Taliban militants, said Attaullah Khogyani, a spokesman for the Nangarhar provincial governor.
The Afghan soldier was killed in the incident, Khogyani said.
"The cause of the shooting is not clear. An investigation has already begun," he said.