A suicide bomber on a motorcycle killed at least 21 people, including three NATO service members and two Afghan police officers, in an attack on a joint NATO-Afghan patrol in the eastern Afghan province of Khost.

Provincial police chief General Sardar Mohammad Zazai told VOA the attacker struck a checkpoint near a busy market, where coalition and Afghan forces were conducting biometric surveys of residents in Khost city, the provincial capital.

The U.S. Embassy in Kabul said three NATO service members and an Afghan interpreter were among those killed in the blast.

U.S. officials said the coalition soldiers were Americans. At least 32 people were wounded, including women and children.

No one claimed responsibility for the bombing. Khost shares a porous border with Pakistan's semi-autonomous North Waziristan tribal region where the al-Qaida and Taliban-linked Haqqani network is said to be based.

The militant group has been blamed for a number of deadly attacks against international forces in Afghanistan.

International combat forces are in the process of withdrawing from Afghanistan and transferring security responsibility to their Afghan counterparts by the end of 2014.