The shooter in Saturday’s incident was an Afghan army commando, Nangarhar provincial spokesman Attaullah Khogyani said. He said the assailant was killed by Afghan forces.
The shootings occurred in the Achin District, where US and Afghan troops have been carrying out a monthslong offensive against a local affiliate of ISIS, officials said.
Taliban spokesman Zabiullah Mujahid said the militants claimed responsibility for the attack.
“A Mujahid (freedom fighter) infiltrator of the Islamic Emirate who had enrolled himself in the Kabul government’s army attacked American soldiers in Lata Band area of Achin district in Nangarhar province today in the afternoon,” said a written statement in Pashto obtained by CNN. “The American invaders were there to support their Afghan slaves.”
US President Donald Trump was briefed on the shootings, a White House spokesman said, but as of Saturday evening there had been no comment from the President.
US Vice President Mike Pence addressed the attack while in Milwaukee on Saturday.
“The President and I have been briefed. Details of this attack will be forthcoming,” Pence said. “When heroes fall, Americans grieve. Our thoughts and prayers are with the families of American heroes.”
A US military spokesman in Afghanistan said the military “will release more information when appropriate.”
Afghan police killed in another incident
In Kabul, meanwhile, the US military command said an unspecified number of Afghan police were killed and wounded in a “friendly fire” incident during a joint Afghan-US operation overnight Saturday.
US Forces Afghanistan said members of the Afghan Border Police in Helmand province were killed and wounded during an operation involving US and Afghan defense and security forces.
The deaths occurred when a US aircraft fired on Afghan police, said Omar Zawak, spokesman for the governor of Helmand.
US Forces Afghanistan is investigating the incident.
Two US service member killed in April
US and coalition casualties in Afghanistan have become rarer in recent years, falling dramatically since the Afghan government assumed responsibility for combat operations in 2014.
Achin District is the primary base of operations for ISIS in Afghanistan and has been the site of multiple joint US-Afghan counterterrorism missions. A US Army Special Forces soldier was killed fighting the terror group there in early April.
Beginning in 2016, Afghan security forces backed by US military advisers launched a major offensive against ISIS. Gen. John W. Nicholson, commander of US Forces Afghanistan, has said the terror group has lost about half of its fighters and been ejected from two-thirds of its territory.
The latest counter-ISIS push began in March of this year.
US officials estimate ISIS has 600 to 800 fighters in the country — mostly former members of other regional terror groups, such as the Pakistani Taliban and Islamic Movement of Uzbekistan. ISIS is believed to be behind a series of terror attacks, including the recent deadly attack on a hospital in Kabul.
There are about 8,400 US troops in Afghanistan. The US counterterrorism mission is separate from the NATO-led effort to train, advise and assist the Afghan army and police force in the fight against the Taliban.
CNN’s Athena Jones and Spencer Feingold and journalist Sune Engel Rasmussen in Kabul contributed to this story.