Eleven people were killed and over 50 others injured, including two German soldiers, at protests in Afghanistan on Wednesday over the deaths of four people in a Nato raid, officials said.
Police opened fire as around 2,000 people took to the streets in Taloqan, capital of the usually peaceful northeastern province of Takhar.
The troubles erupted after NATO-led forces said they killed four insurgents including two armed women in an overnight raid in the town.
A spokesman for the International Security Assistance Force (ISAF) said the raid targeted the Islamic Movement of Uzbekistan (IMU), a militant group that operates from bases including in Afghanistan.
But the protesters claimed those killed during the NATO raid were civilians.
The issue of civilian deaths during foreign military operations is explosive in Afghanistan and has drawn repeated, sharp criticism from Afghan President Hamid Karzai.
During the Taloqan protest, demonstrators threw rocks at the Provincial Advisory Team compound, Afghan interior ministry spokesman Zemerai Bashary told AFP.
The local PAT is a German-led group of soldiers and civilians working to help Afghan government institutions improve their performance.
"We have 11 dead and over 50 other people admitted with injuries to hospital," acting provincial health director Hassan Basij told AFP.
It was not immediately clear whether the casualties were victims of police bullets or from another source.
Two German soldiers were also injured in the disturbances, the country's contingent in Afghanistan said, but did not give details on how badly they were hurt, how they were injured and whether they had intervened in the violence.
Lal Mohammad Ahmadzai, a regional police spokesman, blamed "some opportunists and violence-seeking elements" for infiltrating the protests and turning them bloody.
At the interior ministry in Kabul, spokesman Bashary told AFP: "There have been demonstrations, about 2,000 have demonstrated over the operation overnight. The demonstrations have turned violent."
Although relatively peaceful compared to Taliban strongholds in the south, the north of Afghanistan has seen an increase in violence in recent years.
Seven UN staff were killed when their compound in the northern city of Mazar-i-Sharif was stormed during a protest against the burning of the Koran by an evangelical pastor in the United States.
Afghan and NATO forces have said that central Asian militant groups such as the IMU are active in the region.
ISAF said the operation against the house in Taloqan which triggered the protests targeted a key facilitator for the IMU who was involved in procuring and making weapons and explosives in the area.
It said it was a joint operation with Afghan forces and that weapons including a suicide vest and an AK-47 assault rifle were found at the scene.
All US-led international combat troops are due to withdraw from Afghanistan by 2014 although this month's killing of Al-Qaeda leader Osama bin Laden by US troops in Pakistan has led to calls for this process to be speeded up.
Control of seven more peaceful Afghan areas is due to be handed to the fast-growing Afghan military and police from July.
There are currently around 130,000 international troops, the majority from the United States, stationed in Afghanistan.