Some 25 civilians have died during aerial bombing by foreign forces in the southern Afghan province of Helmand, local residents and senior police say.
Afghan civilians are suffering unnecessarily, Mr Karzai says
The Nato-led force (Isaf) said a small number of civilians may have been killed, possibly by insurgents.
President Hamid Karzai told the BBC this week that civilian deaths caused by foreign forces would have to stop.
If not, Mr Karzai warned that Afghans might turn against those countries with a military presence in Afghanistan.
He added, however, that people were still grateful for that involvement.
Speaking to the BBC's correspondent in southern Afghanistan, people from the village of De Adam Khan, near the town of Gereshk in Helmand, said heavy bombings of the area had resulted in the civilian deaths.
They said nine women and three children were among those killed.
The accounts were backed by the district police chief, and the provincial police chief, Mohammed Husain Andiwal.
Mr Andiwal said Taleban fighters attacked Nato forces first.
"Last night, around 01:30, Nato forces bombed the village... as a result of the bombing 25 people were killed. They included women, three babies between 6 to 10 months one, one mullah of a mosque and other elders."
Mr Andiwal alleged that foreign forces had launched air strikes on the village without consulting with their Afghan counterparts.
Isaf says it is investigating the reports.
An Isaf statement said its forces were attacked on Thursday night near Gereshk and responded with small arms fire and an air strike.
It said that up to 30 insurgents were believed to have occupied a compound and that most of them were subsequently killed.
Isaf said it was trying to determine whether "a small number of civilians" were killed or injured by either insurgents or Isaf action.
In the neighbouring province of Uruzgan, Isaf has said that days of fighting appeared to have caused civilian deaths, some of which might have come from air strikes against Taleban insurgents.
There are two international missions in Afghanistan: Nato's International Security Assistance Force (Isaf), with 37,000 troops from 37 countries including the US. Its aim is to help the Afghan government bring security, development and better governance.
The US-led coalition - under the banner of Operation Enduring Freedom - is a counter-terrorism mission that involves mainly special forces.
The south of the country has this year seen the worst violence since the Taleban were ousted from power in 2001 by US-led troops.