Suspected Taleban fighters have killed 10 Afghan Government forces in a clash near the former Taleban stronghold of Kandahar.
By Paul Anderson
BBC correspondent in Kabul
The killings come as Afghan troops, backed by American-led coalition forces, intensify operations in the southern part of Afghanistan in response to a Taleban resurgence.
Military officials in Kandahar said two vehicles carrying government forces were ambushed by around 16 Taleban fighters who opened fire on them.
Ten soldiers were killed, along with one Taleban fighter and two teenagers who were travelling with the military.
In a separate incident in the same area, four suspected Taleban fighters were killed when American helicopter gunships fired at their vehicle.
The killings are the latest in what has become a daily roster of casualties on both sides.
An American led operation, Mountain Viper, was launched in August in response to heightened activity of Taleban fighters in southern and south-eastern Afghanistan.
Hundreds of people have been killed in the past two months, among them several American soldiers.
President Karzai has accused Pakistani religious extremists, who he believes shelter and support the Taleban.
He has also accused Pakistan of failing to do enough to stop thousands of fighters slipping across the border from their hideouts in the tribal belt to carry out attacks.
Mr Karzai has also called on the international community to improve security in Afghanistan.
Without stability, he says, his country could again become an exporter of terrorism.