Local officials in Kandahar province say the blast occurred in the Spin Boldak district Friday as the five were on their way home from a shrine.
Afghan civilians have increasingly been caught in the middle as violence rises amid an influx of U.S. and other foreign forces fighting the Taliban. A United Nations report this week said the number of civilians killed in war-related violence reached its highest level last year since the U.S.-led invasion in 2001.
In a separate development, a rocket hit the central part of the capital Kabul Friday, near Western embassies. Police rushed to the scene, but no other information was immediately available.
Some information for this report was provided by AP, AFP and Reuters.