An Afghan official said Monday that a man and his two sons were killed by coalition forces after the troops' convoy hit a roadside bomb in Nangarhar province, where U.S. troops are helping Afghanistan's domestic forces battle Islamic extremists.

The U.S. command in Afghanistan said in a statement that a convoy carrying both U.S. and Afghan personnel, "was struck by a roadside bomb and attacked with small arms fire in Nangarhar Province. The convoy returned fire in self-defense and there were no U.S. casualties."

The statement said the U.S. military had not received "official allegations of civilian casualties," but added that any such reports were taken "very seriously and all allegations are thoroughly investigated."

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Attaullah Khogyani, spokesman for Nanagarhar's provincial government, told CBS News that a man and his two sons, aged 8 and 10, were killed by foreign forces who opened fire after the bomb blast. He said an Afghan investigation was underway.

Reports said the incident occurred near the civilian's home in Ghani Khel, a district in the south of Nangarhar, on the border with Pakistan.

U.S. troops have been killed as recently as April fighting Islamic State of Iraq and Syria (ISIS) militants, alongside their Afghan counterparts, in Nangarhar province. The Taliban has also long had a presence in the province.

Near the border with Pakistan, Nanharhar is where the United States in April dropped the largest non-nuclear bomb ever deployed in the battlefield.

The Massive Ordnance Air Blast (MOAB), as it is officially called -- or the "mother of all bombs," as it's become known -- sent a mushroom cloud towering into the air when it was used to target an ISIS tunnel network.

The United States has approximately 9,800 troops in Afghanistan. NATO ended its current mission there in 2014, and but troops remain in the country to assist and train the Afghan Security Forces, though they have been increasingly called on for support.