"Today around noon an Afghan commando opened fire on United States troops in Achin district, killing two American soldiers", provincial spokesman Attaullah Khogyani told AFP. One of those wounded later died of injuries sustained in the attack. "The Afghan commando was also killed in counterattack", he said. According to CBS News, he was a commander of 11-soldier unit. The Taliban claimed responsibility in a statement by Taliban spokesperson Zabiullah Mujahid, who said the attack was committed by one. The group reportedly named the attacker as Obaidullah from Kunar province, releasing a photo purporting to be him.

Mujahid claimed on Twitter that four USA soldiers were killed in the attack.

The incident occurred as USA and Afghan forces returned from a joint operation, the Afghan source said.

There are about 8,400 U.S. troops in Afghanistan.

It wasn't immediately clear if the shooting involved a jihadist sympathizer, a personal dispute or a cultural misunderstanding.

Trump has been briefed by his national security team "on the events occurring in Afghanistan", White House spokesman Sean Spicer said.

Vice President Mike Pence held a listening session in Milwaukee on the impact of the Affordable Care Act on small business and families in Wisconsin.

"When heroes fall Americans grieve", Pence added.

The US Defense Department is conducting investigation, Pentagon said in a statement. One of those wounded later died of injuries sustained in the attack, a USA official tells CBS News.

So-called "green-on-blue" insider attacks by Afghan soldiers on worldwide service members were a major problem several years ago, but now occur less frequently after security measures were improved and the number of foreign troops in the country fell sharply.

Such strikes have bred deep mistrust between local and foreign forces.

The latest counter-ISIS push began in March of this year.

The latest attack comes as US President Donald Trump's administration is considering sending more troops to Afghanistan.

Two U.S. soldiers were killed and two others wounded after an Afghan soldier opened fire on them in eastern Afghanistan on Saturday, according to Afghan officials.

"We would like to express our deepest condolences to the families of the [Afghan Border Police] members affected by this unfortunate incident", a USA military spokesman said in a statement, according to the news service.

An Afghan soldier has killed two USA troops and injured another two in an insider attack.