An Afghan man receives treatment at a hospital after a suicide bomb blast in Khost province June 20, 2012. (Anwarullah/REUTERS)

A suicide bomber targeted an Afghan-NATO checkpoint in the eastern city of Khost on Wednesday, killing 18 Afghans and three American troops, officials said.

Elsewhere in Afghanistan, a roadside bomb detonated, fatally injuring eight Afghan civilians, four of them children.

The governor of Khost province, on the border with Pakistan, said the suicide bomber used a motorcycle to stage his attack on the checkpoint, along a road in a crowded part of town.

Two women, a child and at least two Afghan police officers were among those killed, the governor said in a statement. The Associated Press, citing information from the U.S. Embassy in Kabul, said three U.S. service members and an Afghan interpreter also were among the dead. Thirty-five Afghans were wounded.

Also Wednesday, four children and eight Afghan adults were killed by a roadside bomb that ripped through the tractor in which they were traveling, the Interior Ministry said. 

On Tuesday, Taliban suicide bombers struck a NATO camp, and guerrillas with the extremist group launched a raid targeting a NATO-Afghan checkpoint in southern Kandahar province. Three Afghan police officers died in those attacks, and some NATO soldiers were wounded.