The Central Bank of Nigeria (CBN) has been pumping US dollars into the market at bi-weekly auctions to help support the local currency but without any sustained success.

CBN Gov. Lamido Sanusi said there was no change in the foreign exchange stability stance for now but the bank would not support the naira at all costs.

"Certainly if we do continue to see threats to oil price, if we do continue to see threats to the reserve position and if we think we have exhausted the limits of monetary intervention, we will have to do that and we will have to announce but if there's going to be a depreciation, its something we want to be in control of and we want to be the ones that will announce it," Sanusi said on CNBC Africa television.

"At the moment, the pressure is coming from a number of sources. There are questions about security, there are questions about the expansionary fiscal position for 2012 and of course there are the international issues." 

The CBN broke its own target of keeping the naira within 3 percent above or below 150 to the US dollar again on Wednesday, after breaching the band for the first time last week, further deepening the naira's decline. 

CBN sold $400 million at 155.40 at the bi-weekly auction on Wednesday, short of the $685.37 million demand. The local currency was trading at 162.25 to the dollar in the interbank market, it weakest ever, following Sanusi's comments.

By pumping dollars into the system the CBN is dipping into Nigeria's foreign reserves, which are built up through the sale of its crude oil. Any dip in oil prices due to a slowdown in global economic growth could put pressure on the CBN to stop using oil savings to support the naira.

Foreign exchange reserves fell to $31.7 billion by end-September, the lowest in 13 weeks.

The IMF said earlier this year that the naira was overvalued and that a more flexible approach to currency control would cushion external shocks to sub-Saharan Africa's second-largest economy.

Sanusi has said a stable exchange rate is crucial for maintaining price stability and attracting foreign investment and CBN has been raising interest rates for more than a year to curb high inflation and support the naira.

He said further monetary steps would be taken because of concerns over the euro zone debt crisis and expanding public spending, which Sanusi has highlighted as a problem since his arrival as CBN governor. 

Nigeria's government announced a 2012 fiscal strategy this week which has been put before lawmakers, raising overall spending and assuming ambitious oil output of almost 2.5 million barrels per day (bpd) and a benchmark price of $75.

The fiscal plans also said fuel subsidies would be removed next year, a policy likely to put upward pressure on inflation in the near-term but something advocated by Sanusi.

"If we got an expansionary fiscal policy, combined with structural bottlenecks and we are just coming out of an accommodative monetary stances coming out of banking crisis you would expect the currency to come under pressure," he said.

"In the short term, we will take some monetary measures, we will try to avoid administrative measures and we will try to avoid certainly any kind of capital controls."

The last of nine banks rescued in a $4 billion 2009 bailout got recapitalization approval last week, bringing to a close a reform program set-up two years ago to end the country's banking crisis.

Sanusi said the state "bad bank" AMCON, which controls some nationalized lenders, would issue bonds to rescued lenders in the next two weeks and said the banking crisis was "behind us".