The shooting occurred after a combined U.S.-Afghan force completed a mission at the Shirzad district headquarters in Nangarhar province.
Two United States soldiers and an Afghan trooper were killed Sunday when an individual wearing an Afghan uniform opened fire on them with a machine gun in eastern Afghanistan.
According to official sources, six other army men were injured as the shooting occurred after a combined U.S.-Afghan force completed a mission at the Shirzad district headquarters in Nangarhar province.
"Current reports indicate that an individual in an Afghan uniform opened fire on the combined U.S.-Afghan force with a machine gun," U.S. Colonel Sonny Leggett confirmed in a statement, adding that they "are still gathering information, but the cause of the attack is unknown at this time."
The Taliban have not claimed responsibility for the attack and senior officials were investigating whether it was an internal assault, often known as "green on blue" attacks, which have been usual during the conflict in Afghanistan.
Two U.S. soldiers killed yesterday in Afghanistan have been identified As— Farzana Shah (@Jana_Shah) February 9, 2020
Sgt. 1st Class Javier J. Gutierrez, 28, of San Antonio, Texas, and Sgt. 1st Class Antonio R. Rodriguez, 28, of Las Cruces, New Mexico.#Afghanistan
U.S. Afghan armies fired at each other yesterday pic.twitter.com/ulZUmzaca5
The Pentagon identified the U.S. soldiers killed as Sergent 1st Class Javier Jaguar Gutierrez, 28, of San Antonio, Texas, and Sergent 1st Class Antonio Rey Rodriguez, 28, of Las Cruces, New Mexico.
A member of the Nangarhar provincial council Sohrab Qaderi said the attacker was an Islamist fighter who had infiltrated Afghan security forces participating in the joint operation, but he did not say which group the militant belonged to.
Nangarhar, which shares a long border with Pakistan, has long served as a stronghold for the Islamic State militant group, although the Taliban also has control over parts of the province.
Around 14,000 U.S. troops are stationed in Afghanistan as part of the U.S.-led NATO mission to train, assist and advise Afghan forces and conduct counterterrorism operations.
Despite talks with the Taliban resumed after President Donald Trump abruptly halted negotiations with the insurgents, Afghanistan continues to be Washington’s longest conflict.
The war started following the Sept. 11 attacks in 2001 when the U.S. invaded Afghanistan as part of the so-called "war on terror," to dismantle Al-Qaeda by removing the Taliban from power. More than 220,000 people have died as a result of the invasion.