An unknown number of civilians have died in a US drone strike in the restive eastern Afghan province of Nangarhar, Afghan officials and news agencies report.

Mohammad Ali, police chief of Achin district, where the attack occured, said 15 militants and three civilians died in the incident.

"They were in a house to visit someone who had just come from the Hajj pilgrimage," he said. "A drone targeted the house and killed most of them."

Local politician Esmatullah Shinwari said that at least 12 people had been wounded in the strike on the house, where people had gathered to welcome back a tribal leader from his pilgrimage to Saudi Arabia.

Provincial police spokesperson Hazrat Hussain Mashriqiwal contradicted these reports, saying that no civilians were among the strikes' victims.

A US military command official in Kabul confirmed that a counter-terrorism strike had taken place, and said an investigation into the claims of civilian casulties is underway.

Isis holds some territory in Nangahar, which borders Pakistan, where hundreds of militants are thought to be based. The US has targeted Achin in strikes for months.

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Civilian casualities in US air strikes against Taliban and other militants in Afghanistan have long been a source of friction between the US and allies who have been fighting to end mliltant opposition to the Kabul government since 2001.

In October 2015, a US strike hit a Doctors Without Borders hospital in the northern city of Kunduz, killing 42 people and injuring 30. Doctors without Borders accused the US of a war crime. Cockpit recordings from the planes that carried out the strike showed that the crew questioned the mission's legality.