MTN Nigeria have been given two weeks to pay a $5.2 billion fine imposed on the mobile phone company for failure to cut off users with unregistered SIM cards.
Nigerian Communications Commission (NCC) imposed the penalty on Monday, hitting Africa's biggest mobile phone operator's stock price. Nigeria is MTN's biggest market by subscribers.
NCC spokesman Tony Ojobo said MTN had until Nov. 16 to make the payment, but the two sides were in talks to resolve the matter. "The outcome of the discussion may affect the date. That's why they are having the discussion so that they can reach a solution," Ojobo said.
According to some analysts the size of the fine risked destroying Nigeria's efforts to shake off an image as a risky frontier market for international investors.
Nigeria's presidency and internal security agency were also involved in the talks, a regulatory source said.
MTN shares, up 3 percent at 159.03 rand by 0955 GMT in a slightly higher JSE Top-40 index, have slumped about 20 percent since Monday, knocking more than 60 billion rand ($4.4 billion) off the company's market value.
If it stands, the penalty would wipe out more than two years of MTN's annual profits.
MTN had said on Monday the NCC imposed the fine for failing to disconnect subscribers with unregistered or incomplete SIM cards, under a directive given to all network operators which the regulator said only MTN had failed to comply with.