KABUL, Afghanistan  Afghan officials said Monday that 52 people were killed in southern Afghanistan on Friday when a rocket fired by coalition forces slammed into a house where women and children had taken shelter from fighting between NATO troops and militants. But American officials disputed the account.

If founded, it would be one of the worst cases of civilian casualties in the nine-year war, coming as a leak of thousands of military documents on Sunday casts new scrutiny on whether American and coalition forces have taken enough care to avoid civilian deaths, and whether all of them have been reported by the military.

The Afghan government said its information about the reported attack, which took place in the Sangin district of Helmand Province came from its own intelligence service, the National Directorate of Security.

But late Monday, the American-led military command in Kabul said that an investigation it was conducting with Afghan officials “has thus far revealed no evidence of civilians injured or killed.” But it was not immediately clear whether the NATO investigative team had yet reached the scene.