According to senior police officer Bahadur Khan, the remote-controlled bomb went off on Thursday evening while the policemen were dining.
"The four police were killed on the spot," Khan said. The injured had been taken to a hospital in the provincial capital of Lashkarga.
The rugged countryside of Afghanistan has been witnessing an upsurge in violence in recent months. Much of the violence is attributed to remnants of the Taliban and members of the al-Qaida.
Though driven out of Kabul by US-led forces in 2001, the Taliban have regrouped and threatened more attacks on symbols of the government.