"There has been a suicide bombing. The provincial police chief has been killed," said General Daud Daud. "Two other people have (also) been killed, eight others including police have been injured."

He added that the death toll could rise, saying: "This is what we have right now but it could change and increase."

Police chief Abdul Rahman Sayedkhaili, whose deputy was also wounded in the suicide bombing, was watching firetrucks cleaning the road when the blast happened on a public street, Daud said.

"The bombing was a suicide bombing carried out by an individual on a motorbike," he added.

Afghan police and army officers are frequently targeted in attacks by the Taliban and other insurgents who have been waging war on pro-government forces since being ousted in 2001.

There are around 140,000 international troops in Afghanistan, around two-thirds of them from the United States.

Responsibility for security across the country is due to be handed to Afghan forces in a process due to start in July and be completed in 2014, allowing foreign combat forces to withdraw.