Regulators cite the dangers of speculative trading.
The Nigerian Senate wants Central Bank Governor Godwin Emefiele and chief securities regulator Lamido Yuguda to testify about cryptocurrencies.
The Central Bank of Nigeria said its warning to banks on Friday was not a new position, but a reiteration of its 2017 stance on cryptocurrencies.
Nigeria's central bank told financial institutions they couldn't provide crypto companies or users with services on Friday.
Bolivia is one of the rare countries that has essentially banned cryptocurrency, but the nation's blockchain advocates aren't giving up.