African telecommunications giant MTN is denying allegations in the Nigerian Senate that it illegally exported $14 billion from its biggest market on the continent in the past 10 years.

Ferdi Moolman, CEO of the group's Nigeria operation, says he has Central Bank of Nigeria certificates proving authorization to repatriate the money, based on dividends from capital imported into this West African nation. His statement follows his appearance Thursday before a Senate committee.

Shares of the South Africa-based multinational slumped Friday to a six-year low of 107 rand ($7.64).

Nigeria faces foreign currency shortages caused by slumped oil prices.

In June, MTN Nigeria settled for a much-reduced $1 billion fine for failing to register cellphone SIM cards. It had to cut off some 11 million customers.