MTN Group shares plunged on Thursday following sanctions imposed on the company by the Nigerian government.
Reuters reports that the group's shares plunged to a nine year low by noon Thursday.
The development comes a day after Nigeria ordered the telecoms group to repatriate $8.1 billion that the Central Bank of Nigeria (CBN) said was illegally sent abroad.
The fine comes two years after MTN, Africa's biggest telecoms company, agreed to pay more than $1 billion to end a dispute in Nigeria over unregistered SIM cards.
The CBN said MTN repatriated the money based on illegally issued Certificates of Capital Importation (CCIs) with the 'connivance' of Standard Chartered Bank, Stanbic IBTC, Citibank and Diamond Bank between 2007 and 2015.
The apex bank said the transaction was a "flagrant violation of extant laws and regulations of the Federal Republic of Nigeria, including the Foreign Exchange (Monitoring and Miscellaneous Provisions) Act, 1995 and the Foreign Exchange Manual, 2006'.
Consequently, the four banks were asked to refund various amounts totalling N5.87 billion.
Standard Chartered was asked to refund N2.5 billion; Stanbic IBTC (N1.9 billion); Citibank (N1.3 billion) and Diamond Bank (N250 million).
But a defiant telecom firm, in a reaction to the sanctions, said it will vigorously defend its position on the issue, describing the sanction as regrettable.
"MTN Nigeria, as a law-abiding citizen of Nigeria, is committed to good governance and to abiding by the extant laws of the Federal Republic of Nigeria.
"The re-emergence of these issues is regrettable as it damages investor confidence and, by extension, inhibits the growth and development of the Nigerian economy.
"We will engage with the relevant authorities and vigorously defend our position on this matter and provide further information when available," the telecom firm said in a statement sent to PREMIUM TIMES.
The Nigerian market, considered to be the company's most lucrative market, is said to be the company's most 'problematic'.
As at noon Thursday, the company shares had plunged as much as 23 per cent.