A suicide bomber in police uniform killed ten Afghan policemen and wounded ten others at a checkpoint near the southeastern town of Spin Boldak.
The bomber had been sitting among the policemen as they waited for lunch.
A Taliban spokesman claimed responsibility for the attack. "It was a suicide bomb. Our Talib wore a police uniform and killed more than 15 policemen," a spokesman said.
Spin Boldak is on the border with Pakistan and sits astride the main road into the southern city of Kandahar and a frequent target of Taliban attacks.
In a separate incident, an explosive device killed one soldier and wounded two more from the Nato-led International Security Assistance Force (ISAF) in eastern Afghanistan, the force said.
ISAF has around 38,000 troops based in Afghanistan, while the United States has between 10,000 and 13,000 troops in a separate force.