At least nine Afghan policemen have been killed in an ambush blamed on the Taleban, officials say.
The security forces have come under increasing pressure recently
The attack is the latest in a series of confrontations marking a sharp deterioration in security in the country.
News of the attack coincided with subdued celebrations for Afghanistan's Independence Day.
An explosion in the house of the brother of President Hamid Karzai revived fears of rebel attacks.
The latest attack on Afghan police took place in Kharwar district of Lowgar Province on Monday, a regional military
"Their car was ambushed by Taleban. In this attack the security commander [of Lowgar] and his eight other police officers were killed," Fazlullah Mujadadi told the AFP news agency.
He said they had come under attack on their way back from investigating another attack blamed on the Taleban.
The BBC's Ian MacWilliam in Afghanistan says government officials routinely blame such attacks on the Taleban.
But he says that if the Taleban are behind the attack, it suggests their insurgency is spreading as most of their attacks so far have taken place in tribal lands bordering Pakistan.
On Monday, three government soldiers were killed in an attack in the south-eastern province of Paktika.
The deaths followed a battle in the same area on Sunday, in which more than 20 people were killed.
There have been low-key celebrations on Tuesday in the country to mark Afghanistan's Independence Day.
It commemorates the day in 1919 when the UK gave up control of Afghanistan's foreign relations following a short border war.
The southern city of Kandahar has seen a revival of Independence Day as a holiday in recent years.
But the central government in Kabul has banned elaborate celebrations in Kandahar because of security fears.
Nevertheless, the city held musical concerts during the night and the city streets were decorated with coloured lights.
An explosion in the house of President Karzai's brother about midday revived fears of possible attacks. But the brother, Ahmed Wali Karzai, said the explosion was caused accidentally when some weapons were being moved.
He said one man was injured.
Kandahar province has been troubled by a Taleban insurgency in recent months. The local authorities say this is being encouraged by elements across the border in Pakistan.
Kandahar was the homeland of the Taleban and the movement still has popular support in the rural areas here.
Our correspondent says this is partly because of the villagers' religious conservatism but also because they say the Taleban brought strict law and order.