In a statement today, UNAMA calls for an independent investigation.
The US military told The Associated Press yesterday it had been conducting air operations against Islamic State group loyalists in Nangarhar's Achin district at the time.
Spokesman Brig. Gen. Charles Cleveland said the claims of civilian casualties were being investigated. He had no further details today.
UNAMA says the strike happened as a crowd gathered at the home of a tribal elder to welcome him back from his pilgrimage to Saudi Arabia to perform the Hajj ritual.