Afghan officials say a suicide bombing in the eastern city of Khost has killed at least 20 people, three of them NATO soldiers.
NATO has not confirmed the soldier's nationalities but correspondents say United States troops operate in the area.
Taliban insurgents say they carried out the attack, which also killed six Afghan police and at least 10 civilians while wounding 60 others.
The BBC's correspondent in Kabul says the bomber targeted a coalition convoy passing through a crowded part of Khost. Witnesses say the attacker waited for troops to leave their vehicles before detonating the bomb.
Khost, like other parts of eastern Afghanistan, has experienced a dramatic rise in violence.
In June, a suicide bomber killed 21 people including three US troops and a local interpreter in the city. The attacker drove a motorcycle laden with explosions to a joint Nato-Afghan military checkpoint set up in a crowded bazaar.
The Taliban-affiliated Haqqani network regularly mounts large-scale attacks and suicide bombings in the area.
Over the weekend, a shooting at a checkpoint in eastern Afghanistan took the US military's death toll in the war past 2000.