The international force in Afghanistan declined a request by The Associated Press to comment on the purported strike.
The Afghan official said on Monday that the NATO airstrike came during an operation that was meant to arrest drug smugglers. The official spoke on condition of anonymity because he was not authorized to talk to the media.
He says four other officers from the counter-narcotics team were wounded in the airstrike, which took place on Sunday night outside of Lashkar Gah, the provincial capital in Helmand.
Nabi Jan Mullahkhail, Helmand provincial police chief, confirmed the airstrike but did not say who carried it out or give any other details.