Abuja — Nigeria’s central bank has ordered four banks to refund $8.134bn that MTN illegally sent out of the country in breach of foreign exchange regulations, the central bank said on Wednesday.

The Central Bank of Nigeria has also fined the banks, it said on its official Twitter account, although the fines are small compared to the demanded refund.

Standard Chartered was fined 2.4-billion naira ($7.86m), Stanbic IBTC Bank 1.8-billion naira, Citibank 1.2-billion naira and Diamond Bank 250-million naira.

The Nigerian telecommunications regulator, Citibank, Standard Chartered and Diamond Bank were not immediately available for comment. A spokesman for MTN declined to comment, while a Stanbic IBTC spokesman said a statement would be issued shortly.

Last November, Nigeria’s Senate approved a report largely exonerating MTN, following an investigation after the business was accused of illegally repatriating $14bn to its parent company.

At the time, the Senate also asked Nigeria’s central bank to sanction Stanbic IBTC "for improper documentations in respect of capital repatriation and loan repayments" on behalf of MTN.

Parliament’s upper house agreed in 2016 to investigate whether Africa’s biggest telecoms firm unlawfully repatriated $13.92bn from Nigeria, its most lucrative market which generates a third of its revenue, between 2006 and 2016.