The hostel, located in Pakur's Lamda village, had no security. The 20-strong group had struck late on Sunday night and carried off the girls to a nearby forest.
While nine of them raped the girls for around two hours, the others guarded the institute's gates so no one could come to the rescue of the victims.
"A special policy ensuring the security of schools and institutions located in rural areas is being planned," Soren said.
The government, he added, would bear the costs of the treatment and education of the girls, who belong to the Paharia primitive tribal group.