The Nigerian naira weakened slightly to 150.70 to the dollar on the interbank market on Wednesday from 150.60 close on Tuesday on the back of strong demand for the greenback by fuel importers, traders said.

The central bank sold $250 million at 138.75 naira to the dollar at its bi-weekly forex auction on Wednesday, short of the $267.17 million demanded. The regulator had sold $200 million at 148.75 a dollar at the last auction on Monday.

Dealers said strong demand from gasoline importers and other corporates had put pressure on lenders' dollars reserves, leading the naira to weaken.

"We expected the naira to weaken further this week due to dwindling dollar liquidity at the interbank market, but it could strengthen next week on the expectation of month-end sales by energy companies," one dealer said. Many energy firms are expected to start their usual month-end dollar sales next week, which could provide support for the local currency.

Meanwhile Nigeria's foreign exchange reserves rose around 3 percent to $38.2 billion by mid-August from $37.1 billion at the end of last month, the central bank said on Wednesday.

Forex reserves in Nigeria stood at $43.3 billion a year earlier, but have fallen sharply since then due to demand pressure from importers and a reduction in accruals from oil export revenues. Nigeria's central bank said the present level could finance more than 17 months of import bills in sub-Saharan Africa's second-biggest economy.