By Alastair Leithead
BBC News, Kabul
The Afghan president has described a car bomb attack which killed at least 21 people in Kandahar province as a "cowardly act".
The car bomb was apparently a suicide mission
Hamid Karzai said the Afghan people were grieving after the suicide bomb attack on a market in the town of Panjwayi in southern Afghanistan.
Officials say civilians, including children, were deliberately targeted.
Mr Karzai also expressed condolences to the families of four Canadian soldiers killed elsewhere in Kandahar on
Earlier this week British and Canadian-led forces, belonging to Nato's International Security Assistance Force (ISAF), took control of military operations in southern Afghanistan from US-led coalition troops.
The area has become a stronghold of the Taleban.
Hundreds of people have been killed there in fighting in recent months.
President Karzai thanked the international community for their continuing support for the rebuilding and reconstruction of Afghanistan, and for putting the lives of their soldiers at risk.
A convoy of Nato troops was moving through the Panjwayi area when the car bomb attack took place, but was unaffected, an alliance spokesman said.
Attack in Kabul
Meanwhile a senior police official said 12 Taleban fighters had attacked a police checkpoint inside Kabul's city limits.
President Karzai called the bombers "cowards"
He said one of the attackers had been killed in the assault on the police post near the southern gates to the city, on the Kabul to Kandahar road.
The Taleban are often blamed for local disputes or politically motivated attacks, and it has not been confirmed as to whether they were Taleban fighters.
A spate of bomb attacks in Kabul a few weeks ago initially blamed on the Taleban, now appear to have been caused by different anti-government elements.