Nigeria will start enforcing its stamp duties law on financial transactions across commercial banks, the central bank said in a circular on Tuesday, in a bid to shore-up non-oil revenue and plug shortfalls caused by the drop in global price of crude.

The circular was addressed to commercial lenders whom it said should immediately start charging 50 naira ($0.2513) on every 1,000 naira deposit or electronic transfer conducted by customers.

Africa's top oil producer, which has the continent's biggest economy, relies heavily on revenue from crude sales but the falling oil price means it will have to look elsewhere to fund its budget.

Nigeria plans to spend about 6 trillion naira in 2016 with expected revenue of around 3.9 trillion naira, of which only 820 billion would come from oil.

($1 = 199 naira)