MTN Group Ltd.’s credit rating was cut one level by Fitch Ratings Ltd because of the increased risk that Africa’s largest phone company faces in its two biggest markets, Nigeria and South Africa.

The rating was cut to BBB-, Fitch Ratings said in a statement on Thursday. The outlook was raised to stable from negative.

In Nigeria, Africa’s largest economy, the telecommunications regulator has fined MTN $3.9 billion for failing to switch off unregistered mobile-phone customers.

The fine was revised down from an original penalty of $5.2 billion.

South Africa’s credit rating was cut by Fitch last week because of a worsening growth outlook that threatens fiscal credibility.

“These changes result in increased credit risk to MTN, given its reliance on emerging markets and its exposure to South Africa and Nigeria, in particular,” Damien Chew, an analyst at Fitch, said in the statement.

“An upgrade is unlikely in the short term due to MTN’s significant exposure to countries with high political and regulatory risk.”

MTN Group Chairman Phuthuma Nhleko has been running the company since Chief Executive Officer Sifiso Dabengwa resigned last month and he’s in talks with the Nigeria Communication Commission over the fine. The company’s value has dropped by about a quarter since the penalty was announced in October.