3 US soldiers killed by Afghan force: Official

One American official said the soldiers were shot in an apparent insider attack, also known as a "green-on-blue" because of the color-coding system used by NATO. During such assaults, members of the Afghan security forces are known to target US and other NATO soldiers.

The shooter in Saturday's incident was believed to be a member of the Afghan military, the US official said.

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."

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.

While in Milwaukee, Vice President Mike Pence said: "On my way here, I was informed that US service members were killed and wounded in an attack in Afghanistan. The President and I have been briefed. Details of this attack will be forthcoming. When heroes fall, Americans grieve. Our thoughts and prayers are with the families of American heroes."

A US military spokesman in Afghanistan said: "We are aware of an incident in Eastern Afghanistan. We will release more information when appropriate."