Afghan police say the death toll has risen to 18 from a roadside bomb that exploded in southern Afghanistan on June 20.
Officials said a van carrying an Afghan family was driving along a road in the Marjah district of Helmand Province when it struck an improvised explosive device (IED).
A relative of the family, Mohammad Salih, said the relatives had fled the district in recent days after receiving news about a possible government offensive could be held there.
Nabil Jan Mullahkhail, the provincial police chief, said women and children were among the dead.
No one immediately claimed responsibility for the blast but the Taliban has routinely planted IEDs to target Afghan security forces.
The UN Assistance Mission in Afghanistan said in February that there were more civilian casualties in the country during 2014 than any year since 2009.
It said Taliban and other Islamic militants were responsible for 72 percent of all civilian casualties.