From the BBC:

Afghan clash 'kills police chief'

The provincial police chief and at least eight other police have been killed in a clash with US-trained Afghan guards in Kandahar, reports say.

The clash is said to have erupted after the guards, who are employed by US special forces, tried to remove an Afghan prisoner from a civic building.

The situation remains confused, with Kandahar city closed off.

Kandahar province is a Taliban stronghold, but there is no suggestion the Taliban were involved. ...

Gun battle

The guards are said to have tried to free one of their colleagues who was being kept prisoner at the prosecutor's office in Kandahar City. ...

The BBC in Afghanistan has been told that what began as a fist fight with police turned into a gun battle.

Ahmad Wali Karzai, head of Kandahar's provincial council and a brother of Afghan President Hamid Karzai, confirmed the incident.

"The police chief for Kandahar, the head of the city's criminal department and seven other police were killed in the clash," he told Reuters news agency.

A BBC update, later today, says:
Afghan guards held after shootout

Forty-one US-trained Afghan guards have been arrested after a shootout in which Kandahar's provincial police chief was killed, the regional governor says.

Thoryalai Wesa says the guards will be sent from the southern province to the capital Kabul for trial.

Up to eight other policemen were killed after the guards, who are employed by US security forces, entered the prosecutor's office in Kandahar city.

They were trying to free colleagues held in the building, the BBC was told.

Afghan President Hamid Karzai said he "seriously condemns this action", describing it as a "serious blow to governance-building".

Gun battle

In a statement, Mr Karzai's office described what had happened.

"Armed men from one of the private security firms based in Kandahar tried to free two criminals - they attacked the local prosecutor's office," it said.

"The police chief of Kandahar and the head of the criminal investigation department resisted them - these guards opened fire" and killed them, it went on.

The statement said three others were also killed, although other reports put the total at nine.

The police chief has been named as Matiullah Qatay and the head of the criminal investigation department as Abdul Khaliq Hamdam.

The US military spokesman in Kabul, Col Greg Julian, confirmed to the AFP news agency that there had been "an incident" but did not have details.

Some witnesses had said US forces were at the scene of the incident, but this is unconfirmed.

...

The BBC's Martin Patience in Kabul says that Afghan guards are often employed at coalition military bases across the country.

They are paid and trained by the US. While the guards are recognised by the Afghan government, they do not come under their command.

Locals often refer to these guards as Afghan special forces as they are well-trained and well-armed, our correspondent says.