JALALABAD, Afghanistan (AFP) - An Afghan father and his two young children were killed on Monday (June 12) when US troops opened fire after their convoy hit a roadside bomb, local authorities said.

The civilian and his sons, aged seven and 10, died near their home in the eastern province of Nangarhar, where American forces are conducting joint operations against militants from the Islamic State in Iraq and Syria (ISIS) group.

Claims of civilian casualties remain a contentious issue in the war against insurgents in Afghanistan, as President Donald Trump mulls sending more troops into the lengthy conflict.

"A roadside bomb hit a foreign forces convoy in Ghani Khail district this morning," said provincial spokesman Attaullah Khogyani.

"The troops then opened fire and killed three civilians nearby, a father and his two sons."

The account was confirmed by the district police chief, Sekandar Safi.

The US military confirmed they opened fire in "self defence" but said they had so far not received any official allegations of civilian casualties.

"We take civilian casualties very seriously and all allegations are thoroughly investigated," the military said in a statement. "The incident is under investigation and more information will be released as appropriate."

Nangarhar is a stronghold of Islamic State in Iraq and Syria (ISIS) and Afghan forces backed by US troops have been battling for months to drive them out.

On Saturday (June 10), three American soldiers were killed and one wounded when an Afghan commando opened fire on them in Nangarhar's Achin district, in an insider attack claimed by the Taleban.

In April, the US military dropped its largest non-nuclear bomb ever used in combat on a complex of caves in Achin used by ISIS fighters.

The deployment of the so-called Mother Of All Bombs killed dozens of Islamists, but fighting in the area has continued unabated.