An Afghan rights group says a U.S. air strike in western Afghanistan earlier this month killed up to 97 civilians.

Afghanistan's Independent Human Rights Commission (AIHRC) says its investigation shows that of those killed, 21 of the victims were women, and  65 were children.

The air strike took place in the Bala Bulak district of Farah province on May 4 and 5.

The commission says most of the deaths took place in three houses were civilians had gathered.  

An earlier investigation by the Afghan government found that as many as 140 civilians had been killed. However, the AIHRC says the government investigation was conducted too quickly.

An investigation by the U.S military placed the number of civilian deaths between 20 and 30, adding that around 60 insurgents were killed in the operation.

U.S. officials have said that it may be impossible to determine the exact death toll because all the bodies were buried before investigators arrived on the scene.

The AIHRC report says that witnesses and government officials report that between 25 and 30 insurgents were killed. However they say it is unclear whether their deaths took place during the initial fighting or subsequent air strikes.

The AIHRC says it is continuing its investigation of the incident.

Some information for this report was provided by AFP and Reuters.