An official says a bomb attached to a donkey has exploded, killing a policeman and wounded three civilians.

Local government spokesman Sarhadi Zwak says the donkey blew up in front a police security post in the Alingar district of Laghman province.

He says Taliban militants carried out Friday's attack.

Insurgents are finding new ways to thwart stepped up security measures in their bid to undermine confidence in the Afghan government, as U.S. and other foreign combat forces prepare to withdraw by the end of 2014.