Nine US soldiers have been killed in Afghanistan, in one of the biggest losses of life in a single incident since operations there began in 2001.
The troops died when insurgents attacked a military outpost in the north-eastern province of Kunar, close to the border with Pakistan.
The fighting came as international and Afghan forces battled militants on several fronts.
One soldier from the US-led coalition was killed by a bomb in Helmand.
On Sunday, US forces said 40 insurgents had been killed in Helmand province in 24 hours.
A statement from Nato's International Security Assistance Force (Isaf) said the nine were killed in several hours of fighting in a mountainous area in Kunar province.
It said 15 more Isaf soldiers were wounded along with four Afghan troops.
Isaf currently has 53,000 troops from 40 countries.
Insurgents used rockets, mortars and machine guns to attack the remote Afghan army and Nato outpost.
Isaf and Afghan National Army forces responded with small arms, machine guns, mortars and artillery, the statement said.
Fighter jets and Apache helicopters were also deployed. Reports quoting Afghan officials say there may also have been civilian casualties.
Nato says the rebels suffered heavy casualties. It did not name the attackers but there has been a sharp increase in Taleban attacks in the country, and in that region in particular.
The BBC's Martin Patience in Kabul says Afghanistan's north-eastern border with Pakistan is a well-known trouble spot.
The fighting is close to where US forces were accused of killing 47 civilians in an air strike in Nangarhar province a week ago.
The US military said they were militants.
In a separate incident on Sunday, a suicide bomber killed at least 21 people, many of them children, in a market in the Deh Rawud district of Uruzgan province.
No group has claimed responsibility for the suicide bombing.