The attack on Wednesday night was aimed at destroying a hideout used by Islamic State militants, but it accidentally targeted farmers near a field, three government officials told Reuters.
Sohrab Qaderi, a provincial council member in eastern Nangarhar province, said a drone strike killed 30 workers in a pine nut field and at least 40 others were injured.
The defence ministry in Kabul confirmed the strike, but refused to share casualty details immediately.
US forces were not immediately available for a comment.
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