Afghan President Hamid Karzai has accused the United States of failing to fully co-operate with an investigation into the massacre of 16 villagers by a US staff sergeant.
Several investigations are underway by US and Afghan officials into the killings in Kandahar province on Sunday.
Mr Karzai listened to village elders and the families of victims of the massacre at the start of an expected two days of talks to discuss the killings.
He said the Afghan investigation team has not received the co-operation they expected from the United States.
Mr Karzai appeared to back the belief of the villagers that one gunman acting alone could not have killed so many people in different locations some distance apart.
The president also said the problem of civilian casualties at the hands of NATO forces cannot be tolerated.
"This has been going on for too long. You have heard me before. It is by all means the end of the rope here," he told reporters.
Meanwhile, the 38-year-old soldier implicated in the massacre has been named as US Army Staff Sergeant Robert Bales.
He was due to arrive on Friday at the Fort Leavenworth army base in Kansas, where he would be held in a maximum security facility.
The soldier is expected to face justice under US military rules, but it is not clear where any trial would take place.