In March, another Afghan soldier was killed after he fired on us forces at a base in Helmand province, wounding three Americans.
Reuters reports that shortly before Saturday's attack, at least three members of the Afghan security forces were killed by USA aircraft during an overnight raid in Helmand.
The US military initially had issued a short statement saying it was "aware of an incident in eastern Afghanistan".
Trump has been briefed by his national security team "on the events occurring in Afghanistan", White House spokesman Sean Spicer said.
Yesterday's attack came just hours after at least six Afghan policemen were wounded in an errant United States air strike in southern Helmand province. It says the incident is under investigation.
In some cases Afghan troops have been forced to abandon more scattered and rural bases, and the government can claim to control or influence only 57 percent of the country, according to US military estimates from earlier this year.
Afghan authorities April 15 reported a jump in fatalities from the American military's largest non-nuclear bomb, declaring some 90 Islamic State fighters dead, as US-led forces conducted clean-up operations over their mountain hideouts.
Beginning in 2016, Afghan security forces backed by USA military advisers launched a major offensive against ISIS.
Afghan officials initially reported that two USA service members were killed but US officials later said three had died in the incident.
The motivations for such attacks are sometimes unclear, with some resulting from personal conflicts while others may be due to the Taliban's infiltrating the Afghan military. When heroes fall, Americans grieve.
Earlier, a USA airstrike in southern Afghanistan accidentally killed at least two Afghan policemen, according to Afghan officials.
NPR's Amy Held notes that while the USA officially withdrew from Afghanistan in 2014, roughly 8,400 troops remain in the country - and the Trump administration has been considering requests to increase those troop levels. Richard Flynn, of Starke, Fla., of Tactical Command Post, HQ Company, 2-502 Infantry, 101st Airborne Division, take up a fighting position behind a barrier, during a joint patrol with the Afghan Army, in Zhari district, Kandahar province, southern Afghanistan.