Seven Afghan policemen have been killed by US forces in a "friendly fire" incident in the eastern province of Nangarhar, Afghan officials say.
Police show the bloodstains of one of their colleagues
The US military says US and Afghan forces retaliated after coming under fire. It did not confirm the deaths of the policemen.
Elsewhere Nato says its soldiers killed three civilians in Kunar province.
The International Committee for the Red Cross says the security situation in Afghanistan is deteriorating.
In a report marking 20 years of its work in Afghanistan, the ICRC said life for ordinary people in Afghanistan was getting worse.
"It's really had a heavy price in terms of the population, both in terms of wounded and in terms of killed and people displaced so it's a very worrying situation," the ICRC's director of operations, Pierre Kraehenbuhl, said.
Local Afghan police insist that US-led forces opened fire on them first in the friendly fire incident at a security post in Nangarhar province on Monday night.
Speaking to the BBC, a senior police officer, Nasir Ahmad Safi, described the incident as "brutal".
"Last night the Americans attacked our police post in the district and then they asked for air support. They attacked us from ground and air," he said.
That account is disputed by US-led forces who were on an anti-Taleban operation.
"En route to the location the forces were suddenly ambushed from both sides with rocket-propelled grenades and small arms and returned fire and called in air support and broke contact," spokesman Major Chris Belcher said, the AFP news agency reports.
"Following the engagement, the identity of the assailants was called into question. Further details will be released as they become available."
In the capital, Kabul, a spokesman for President Hamid Karzai, Karim Rahimi, supported the American account in what he called a "tragic accident".
"The police checkpoint in the area thought that they were the enemy, so police opened fire on the coalition, and then the coalition thought that the enemies were firing on them, so they returned fire back," Mr Rahimi said, according to the Associated Press news agency.
In the south, meanwhile, Nato says one of its soldiers was killed and two others wounded in an explosion. It did not say what caused the blast.
Separately, in Kunar province, also in the east, Nato-led international forces in Afghanistan said three civilians were killed at a checkpoint on Monday.
Officials said an oncoming vehicle failed to respond either to gestures telling it to stop or a warning shot into the ground.
For many months now there has been a steady succession of incidents involving civilians at checkpoints of the Nato-led multinational force (Isaf), says the BBC's Charles Haviland, in Kabul.
Large numbers of civilians have been killed in an upsurge in violence in Afghanistan in the past two years.
Most have died at the hands of Taleban and allied insurgents, but the deaths caused by the US-led anti-insurgency coalition and Isaf are a highly sensitive matter, our correspondent says.
Afghan officials say more than 50 civilians died in April in joint US-Afghan bombing operations in the west of the country.