One source says the ransom paid to the jihadist group totaled more than 63 million kronor, while another source says it was over 13 million kronor.
The payment violates the country's laws, which prohibit payments to kidnappers.
The board denies that a ransom was paid to the group that kidnapped nearly 300 students and school staff from a Catholic school; at least 50 later managed to escape.
Among those released were two leaders of the group.
Boko Haram has not previously been linked to the kidnapping, but according to AFP's sources, one of the group's leaders is behind it.
