The Central Bank of Nigeria (CBN) has fixed the exchange rate of the naira at N198 per dollar, a move aimed at closing the gap between the parallel and official rates.
The bank abolished its weekly Dutch Auction sales so that foreign exchange seekers could buy from their banks.
The commercial banks have also been warned to desist from reselling CBN dollars to other banks.
The naira is likely to plummet further.
CBN governor Godwin Emefiele had announced a devaluation of the naira from about N155 to N168 per dollar last November.