The AFP and Associated Press news agencies quoted the head of the province's Chaparhar district, Mohammad Sediq, as saying the blast went off as the girls were collecting firewood.
The reports say the girls were between 9 and 13 years old.
An investigation has been launched into whether the girls may have accidently caused the device to explode.
Meanwhile, Afghan police say at least one person was killed and at least 15 injured after a car bomb exploded outside a military contractor's compound on the outskirts of Kabul.
The bomb reportedly blew a large hole in the exterior wall of the compound.
Police chief Ayoub Salangi told Reuters news agency on December 17 that the explosives were placed in a small truck.
The blast happened on the Jalalabad road, near the location of bases housing foreign troops.
Police say the compound belongs to the U.S.-owned company Contrack, which builds facilities for military bases.