The world's newest nation, South Sudan has its own currency, the South Sudanese pound.
Officials in the country had hoped the Khartoum government would take back the old notes collected and give them the equivalent in US dollars but when South Sudan launched its new currency in July - Sudan announced it would do the same a week later.
Officials say they are now sitting on close to $1 billion in currency they cannot use, creating friction between the two neighbouring countries.
Al Jazeera's Haru Mutasa reports from the capital, Juba.
