South Sudan, which declared independence on July 9 under a 2005 peace deal that ended decades of civil war, said last Monday it had started circulating its new South Sudan pound, pegging it one-to-one with Sudan's existing pound .
In a brief statement, the northern central bank said the new currency would go into circulation on Sunday.
It previously said it would take up to three months to replace the old Sudanese pound, describing the currency move as "precautionary measure" following the southern plans.
The Sudanese pound has been falling on the black market in Khartoum for weeks as economists say foreign currency inflows needed for imports will decline alongside falling oil revenues.
The old pound has also fallen in the south on worries the old notes will be worthless if both countries do not reach an agreement to coordinate their currency launches.
The south took about 75 percent of Sudan's 500,000 barrel-a-day oil reserves with it when it left.
North and South Sudan have yet to work out a large range of issues from sharing oil revenues to ending violence in some parts of the joint border.