The bomb went off along a road to the north of Kandahar city on Sunday as the policemen were passing in a vehicle, Mohammad Nabi, a senior provincial official, said.
Aljazeera's correspondent reported that six Afghan policemen were killed on Saturday evening and another five were injured when a bomb hit the vehicle carrying them in Shah Wikot in Kandahar province.
US forces said six Afghan soldiers were killed and eight armed Taliban members arrested during a search campaign by US and Afghan forces in three districts in Helmand province during the past two days of clashes with Taliban fighters.
The statement did not comment on Taliban losses, Aljazeera's correspondent said.
"It was a bomb. It killed six policemen and wounded five," Nabi said of Sunday's roadside bomb-attack, adding that Taliban insurgents were responsible.
Taliban fighters, battling US and government forces since they were ousted in 2001, have claimed responsibility for most of a recent wave of blasts in the Afghan south and east.
The latest attack came 48 hours after the biggest battle in months between the insurgents and US-led and Afghan government forces.
Up to 200 Taliban launched a series of attacks in the southern province of Helmand, to the west of Kandahar, on Friday and fighting raged for hours.
Sixteen Taliban and six policemen were killed, a provincial official said.
US and British aircraft, together with US and Afghan ground troops, eventually beat back the insurgents, the US military said.
Insurgents later killed a government administrator in a nearby district and two civilians were killed in a bomb blast aimed at security forces in Kandahar city on Saturday, police said.
The surge in violence comes as Nato is preparing to expand its Afghan peace-keeping force into the volatile south.
The 9000-strong Nato force will
nearly double in size soon
Several thousand British troops are due to be deployed in Helmand this year and the Dutch parliament voted last week to send 1400 soldiers to Uruzgan province.
Canadian troops, already based in Kandahar, will soon get reinforcements.
Under the expansion plan, the 9000-strong Nato force will nearly double in size.
The US heads a separate international force of about 21,000, made up mostly of US troops, fighting insurgents and hunting for their leaders.
The US is hoping to withdraw up to 3000 of its troops as the Nato peacekeepers take over more responsibilities.