Seven people have died after Afghan police opened fire on demonstrators in Sheberghan, the capital of the northern province of Jowzjan, officials say.
Gen Dostum has fallen out with the regional governor
The demonstrators were supporters of the controversial Uzbek fighter Gen Rashid Dostum.
They were demanding the resignation of the provincial governor. Nato-led troops have been called in.
Meanwhile US-led forces say they have killed 36 Taleban in the south. Locals say most of the dead were civilians.
About 1,000 supporters of General Dostum were protesting outside government offices in Sheberghan. Some reports say they were throwing stones.
Gen Dostum and the provincial governor, Joma Khan Hamdard, used to be close allies, but the BBC's Daud Qarizadah in Kabul says political differences have emerged recently and the two men are now rivals.
As well as the seven dead, more than some 30 protesters were injured in the police firing. At least 10 are reported to be in a critical condition.
Shops in Sheberghan are closed and Afghan soldiers and police have been deployed to keep order. Nato-led forces with tanks have also taken up position in the city centre.
Governor Hamdard told the BBC Pashto service that the protests were organised by Gen Dostum. A spokesman for Gen Dostum in Jowzjan said the demonstration was a "public uprising" against the governor who he described as "incapable".
Gen Dostum is one of the most controversial figures in Afghan politics.
In the 1980s he backed the invading forces of the Soviet Union against the mujahideen rebels. He then played a prominent role in the civil war that destroyed much of the capital, Kabul, and left thousands dead.
In 2001, while helping the US, his militias were accused of suffocating hundreds of Taleban prisoners to death by locking them inside shipping containers.
Elsewhere in Afghanistan, US-led coalition forces say more than 36 Taleban militants were killed after they ambushed a convoy of coalition troops and Afghan police in the southern province of Helmand.
US forces said the convoy hit two roadside bombs and then came under rocket and gunfire from the insurgents.
US troops in Helmand called in air support
In a 10-hour battle, aircraft were called in, destroying a fighting position and killing more than three dozen insurgents, the US said.
However, a number of local people told the BBC that more than 20 civilians had been killed in the bombing raid, including some women and children.
They said there had been no Taleban in the buildings destroyed and said the ambush of US forces had taken place some distance away.
The US coalition denies this, saying no Afghan civilian injuries were reported.
There is no independent verification of either account.
In the south-eastern province of Paktika, Taleban militants are reported to have killed six police officers in an attack on their convoy.
A government spokesman said the militants detonated several bombs as the convoy passed by, and opened fire.
There are also reports of two Taleban suicide attacks, one in northern Kunduz province, and one in Kunar, in the south-east with a number of civilians killed.
Bloodshed in Afghanistan has returned to levels not seen since the fall of the Taleban in 2001, with parts of the south and east particularly hard-hit.
Analysts say the attacks are the Taleban's response to being squeezed by the build-up of foreign troops in the south and east and that they are very difficult to prevent.
Some 4,000 people are believed to have died in 2006 in the insurgency - about a quarter of them civilians.