"This incident is under investigation", the statement added.
What is particularly worrying about this attack is that it occurred in the eastern Afghanistan province of Achin, a stronghold of ISIS forces in Afghanistan. Khogyani said the Afghan soldier responsible for the attack was killed. An overnight United States air strike in southern Afghanistan killed at least two policemen and wounded four others, officials said June 10, the latest in series of "friendly fire" incidents.
President Donald Trump was briefed on the "emerging situation" in Afghanistan, White House deputy communications director Raj Shah said earlier Saturday.
Afghanistan has suffered a string of violent attacks in recent weeks after the Taliban launched their spring offensive, including attacks in the capital city of Kabul that killed and wounded hundreds. Details of this attack will be forthcoming.
"When heroes fall, Americans grieve", Pence said.
The US Defence Department confirmed on Saturday that three US soldiers were killed and another wounded in eastern Afghanistan. A news release from the USA military on Saturday confirmed that an incident had happened in the area overnight in which "personnel from the Afghan National Defense and Security Forces were killed and wounded".
The three previous U.S. soldiers' deaths in Achin make up the entirety of USA combat fatalities in Afghanistan in 2017.
USA and Afghan troops have been battling militants in the Nangarhar province for months.
U.S. and coalition casualties in Afghanistan have become rarer, falling dramatically since the Afghan government assumed responsibility for combat operations in 2014. USA military officials estimate there are about 600 to 800 Islamic State fighters in Afghanistan, mostly in Nangarhar, but also in the neighbouring province of Kunar.
The group once controlled Afghanistan, and has recently regained its influence over Afghanistan.
American troops have partnered with Afghan soldiers in raids against ISIS Khorasan, claiming the local offshoot of the militants group based in Iraq and Syria is steadily losing ground in Afghanistan.