Nato has said it will investigate reports that it has killed dozens of civilians in recent days in ground and air strikes in eastern Afghanistan.
The governor of Kunar province has said 64 civilians have been killed in recent Nato-led air strikes in a remote mountainous district.
Afghan President Hamid Karzai later said more than 50 civilians had died.
Nato claims to have killed more than 30 insurgents in an overnight raid in the area two days ago.
A spokesman for the Nato forces in Afghanistan told the BBC that they had no evidence of any civilian casualties, but that they were looking into the reports.
Governor of Kunar Province, Fazlullah Wahidi, said on Sunday that 20 women and a number of children were among the 64 civilians killed in the district of Ghaziabad over the last few days.
Shortly afterwards, President Hamid Karzai said that, based on information from Afghanistan's spy agency and local officials, troops had killed more than 50 civilians during days of operations.
Mr Karzai said "about 50 civilians have been martyred during international military forces operations in Ghaziabad district in Kunar province," according to AFP, adding that he "strongly condemns" the killings.
He said he had sent a government delegation to the district to investigate the incident.
A statement from the International Security Assistance Force (Isaf) said it took the reports of civilian casualties "very seriously".
"We are conducting an immediate assessment of these allegations and will report our findings," US Army Colonel Patrick Hynes, a senior Isaf spokesman, said in the statement.
On Friday, Isaf said 30 insurgents had been killed in an overnight raid in Kunar, and on Saturday said operations had been continuing in Ghazi Abad since 16 February.
A statement on Sunday said Isaf had killed an "unknown number of insurgents" in two separate operations.
Earlier this month, a human rights watchdog said that 2010 was the deadliest year for Afghans since the war began in 2001.
Afghanistan Rights Monitor said the Taliban were responsible for about 60% of the 2,400 civilians killed, while US-led forces were accountable for 21%.
Last year, the whistle-blowing website Wikileaks leaked a swathe of documents relating to the Afghan war, which suggested that many civilian casualties were going unreported