The naira closed at 158.40 to the dollar on the interbank market, weaker than Friday's close of 158.20 to the dollar.

"Strong dollar demand by some importers toward the end of trading pushed down the naira," one dealer said.

The central bank sold $200 million at 155.80 to the dollar on its bi-weekly auction, compared with $180 million sold at the same rate at the last auction On Wednesday.

The regulator did not disclose the amount demanded at the auction.

Dealers said the upsurge in dollar demand toward the end of trading was driven by importers losing their bids at the auction and diverting to the interbank.

"We see the naira hovering within the present level or strengthening a little on expected dollar inflows from offshore investors participating at the treasury bills auction this week," another dealer said.

Nigeria plans to issue 142.97 billion naira ($903.73 mln) in treasury bills ranging from 3-month to 1-year maturities at its regular twice-monthly auction on Sept. 6.