South Africa's bourse briefly suspended trading in telecoms firm MTN Group on Monday, after the stock fell as much as 8 percent as Africa's largest mobile telecoms operator battles to reduce a $5.2 billion fine it faces in Nigeria.
The stock has fallen more than 25 percent in the past seven sessions, wiping in excess of 60 billion rand ($4.4 billion) off its market value, after the Nigerian Communications Commission (NCC) imposed the fine last week for failure to cut off unregistered users.
After trading resumed hours later, MTN shares were down 5.9 percent at 148.51 rand at 1200 GMT. They earlier touched a three-year low of 142.50 rand.
One trader said the stock tumbled due to speculation the company had agreed to pay the fine, which is equivalent to almost a quarter of Nigeria's 2015 budget of $22 billion and would wipe out more than two years of MTN's annual profits.
"There has been some speculation that the company has agreed to pay the fine, but we really want to hear it from the company itself," said Afrifocus Securities portfolio manager, Ferdi Heyneke.
MTN said the firm was still in talks with Nigerian authorities about the fine.
"The company reiterates that engagements with the Nigerian authorities are continuing," MTN said in statement, confirming a Reuters report earlier.
MTN has been in talks with the Nigerian presidency, internal security agency and the NCC to resolve the matter, according to a regulatory source. MTN Chief Executive Sifiso Dabengwa flew to Abuja to make what three sources familiar with the matter said was an attempt have the penalty reduced.
NCC on Friday gave MTN two weeks to pay the fine.
Nigeria has been pushing the industry to have every SIM card registered on worries that unregistered SIM cards were being used for criminal activity in a country facing Islamic militant group Boko Haram's insurgency.
It was unclear what would happen to MTN, whose Nigerian licence is up for renewal in 2016, if the company fails to pay the fine, but NCC's powers include revoking licences.
Some analysts said the size of the fine risked damaging Nigeria's efforts to shake off its image as a risky frontier market for international investors. Others said the fine showed Nigerian regulators were keen to enforce the law.
The fine, if imposed as it is, would leave MTN with little money to spend on its network in Nigeria, where it the biggest player, said Africa Analysis' Dobek Pater
"Nigeria is stuck between a rock and hard place. It's an astronomical fine that would not only hit MTN profits but also its ability to invest in network, which is vital to Nigeria's telecoms infrastructure," Pater said.
Investors also hammered MTN debt with yields on company's eurobonds soaring to all-time high on Monday. The yield on the $750 million paper due in 2024 climbed to a record 5.975 percent by 0905 GMT, extending gains to 129 basis points since last week.
($1 = 13.7665 rand)