Updated 6:08 p.m. EST
Three U.S. soldiers were killed and one wounded after an Afghan soldier shot them in eastern Afghanistan, the Defense Department confirmed.
The Associated Press initial reported two fatalities, citing Attahullah Khogyani, spokesman for the provincial governor in Nangarhar province, who said the Afghan soldier was killed after the incident in the Achin district.
ABC News later reported the three soldiers were slain in the attack.
A defense official told Military.com that the latest assessments indicated three service members were killed in the incident and one was wounded.
Navy Lt. Damien Horvath, a spokesman for the U.S. military in Afghanistan, initially said, "We are aware of an incident in Eastern Afghanistan. We will release more information when appropriate."
The Pentagon later released a statement saying the three soldiers were killed and one was medically evacuated from the scene. Officials were working to notify the family of the fallen troops, it said.
An investigation into the shooting is underway and additional information will be released as appropriate, the statement said.
The region has seen heavy fighting this year.
Excluding the reported casualties above, four U.S. troops have died in 2017 in Afghanistan. Three of those were combat deaths -- and all occurred in Nangarhar, where Achin is located, according to the website icasualties.org, which tracks American and coalition casualties in the country.
Achin is also the same area where the U.S. dropped the 21,600-pound "Mother of All Bombs," or MOAB, April 13 against a cave and tunnel complex used by fighters of the Islamic State of Iraq and Syria affiliate called Islamic State-Khorasan Province, or ISIS-K.
The U.S. has roughly 8,400 troops in Afghanistan, including a few hundred Marines who this spring returned to the southwestern Helmand province. NATO, meanwhile, has another 4,500 troops in the country.
President Donald Trump hasn't yet decided whether to grant the request by Army Gen. John Nicholson to send thousands more U.S. troops to Afghanistan.