The naira closed at 156.08 to the dollar on the interbank market, firmer than the 156.50 it closed at on the previous day.

The currency has not been at this level since July. 25, when it closed at 156.05.

"The unexpected huge dollar flow from offshore investors further boosted liquidity in the market and help the naira firm further," one dealer said.

Nigeria had sold about 166.39 billion naira ($1 billion) worth of treasury bills with maturities ranging from three months to one year.

The state-run oil and gas company the NNPC sold about $500 million to banks on Wednesday, which fed through the system on Thursday, strengthening the naira, traders said.

Dealers said the naira could peak then depreciate in the near term, as dollar demand from importers after the New Year holiday builds up.

Center>Copyright Reuters, 2013