Pagan Amum said Monday that many Southern Sudanese are still holding old Sudanese pounds. He says the northern government has declared those illegal tender.
South Sudan also released a new currency, also called the pound, shortly after its July 9 independence.
Amum says the north had agreed not to issue a new currency until six months after the south did. He says the move will cost the southern government at least $700 million.
Northern officials could not be reached for comment.
The two countries still have not resolved major issues including a disputed border region, oil management and revenues.