Augusto Blute, a doctor based in the capital who treated several victims, said today the bus was travelling between the towns of Bissora and Encheia in the north of the country when the explosion occurred yesterday.
He said the minibus was completely destroyed, and that the blast was strong enough to render most victims unrecognizable to their relatives.
Local officials say the mine may date to the country's fight for independence from colonial power Portugal.
The country obtained independence in 1974, though it has been roiled by coups and instability since then and no president has ever finished his term in office.