Afghan police say a suicide bomber was responsible for a vehicle explosion near the home of a former police officer in Helmand province.
The blast in Lashkar-gah killed at least five people and wounded some 19 more.
There was no immediate claim of responsibility, although the Taliban often targets security forces and government officials in such incidents.
The bombing comes after last week's signing of a deal to allow foreign troops to remain in Afghanistan.
The agreements will allow 12, 000 foreign soldiers to stay, mostly to carry on training Afghan forces.