The majority of the dead were civilians, among them three women, said Abdul Hakim Esaaqzai, chief of police for Khost province. Health official Amir Badshah said 30 people had been wounded and many taken to hospitals.
The attack targeted a checkpoint at the start of the main road to neighboring Paktia province. Police at the checkpoint identified the attacker as a suicide bomber and shot at him, but not in time to prevent the detonation, Esaaqzai said.
At least one policeman was killed in the blast.
Khost, which borders Pakistan, is an insurgent stronghold where government control is largely limited to urban centers.
Violence across Afghanistan in 2010 reached its worst level since the Taleban were toppled by US -backed Afghan forces in 2001, with civilian and military casualties at record levels.
