Former governor of the central bank of Nigeria Lamido Sanusi has criticized the bank's currency policy, saying Nigeria will have to devalue the naira and loosen monetary policy to revive its economy.

Current CBN Godwin Emefile has ruled out another naira devaluation, saying repeatedly that the currency was "appropriately" priced despite a sharp fall of oil revenues whacking public finances. President Muhammadu Buhari had backed Emefiele's stance.

"It is wrong to think that you can keep the naira at a certain level when the price of oil is falling without depleting your reserves," Sanusi told CNBC television.

"It does not speak well of us to pretend that the naira is appropriately priced," he added.

Sanusi also criticised foreign currency restrictions imposed by the central bank, which have frustrated local firms struggling to get dollars.

"It's time to loosen monetary policy. We need to lower interest rates otherwise we compound an exchange rate crisis for businesses with high borrowing costs and declining demand," Sanusi said.

The central bank had allowed the main benchmark rate unchanged at 13 percent at its last monetary policy meeting in September while cutting the banks' cash reserve ratio to 25 percent from 31 percent.