Local officials said a bomber detonated his explosives in Maimanah, the capital of Faryab Province, on Wednesday as the American troops were filming interviews at a local park.
They said the attacker blew up an explosive-laden motorcycle close to a convoy of US-led forces in the area.
Taliban militants claimed responsibility for the incident.
At least seven US-led troops have been killed in attacks across Afghanistan over the past two days, causing foreign military deaths to pass the 100 mark in the southwest Asian country this year.
Bomb attacks and ambushes targeting foreign troops rise at this time of the year, which is known as the Taliban’s annual spring offensive.
Insecurity continues to climb across Afghanistan, despite the presence there of tens of thousands of US-led troops.
GJH/AS/HN