By BBC News, photo by Getty Images
Shares in Africa's biggest mobile operator were suspended on Monday in the wake of a huge fine imposed by Nigerian regulators.
Trading in MTN Group was halted in Johannesburg after the stock fell by as much as 8%. Its shares had fallen more than 25% since the $5.2bn (£2.7bn) fine was announced last week.
The Nigerian Communications Commission imposed the penalty for failure to cut off unregistered users. It gave MTN just two weeks to pay the fine.
Chief executive Sifiso Dabengwa, who used to run the company's Nigerian operations, is understood to have flown to Abuja in a bid to negotiate a lower penalty.
Negotiations were continuing between the Nigerian authorities and the company on Monday, Reuters reported. Nigeria is MTN's biggest market, with 28.5 million subscribers, followed by Iran and South Africa.
The Johannesburg Stock Exchange said that trading in MTN shares was halted pending an announcement from the company.
"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 Ferdi Heyneke, securities portfolio manager at Afrifocus.
The slide in MTN shares has wiped about 60bn rand (£2.7bn) off its market value, with the company now worth about £13bn.
There's more this story than meets the eye. It's not simply a case of a company failing foul of regulatory authorities and getting a slap on the wrist - some analysts say this $5.2bn slap is enough to break or seriously bruise MTN's wrist.
The fine itself was imposed because MTN failed to cut off unregistered SIM cards, which was regarded as crucial to limiting the communications of Nigeria's various armed criminal and terrorist groups.
It is thought that the kidnapping of a former finance minister, Chief Olu Falae, was the thin end of the wedge for the Nigerian authorities.
He was taken by armed men at the end of the September. It transpired that the phone the kidnappers were using to communicate their ransom demands had an unregistered SIM card from MTN.
That is when the Nigerian government is thought to have finally run out of patience with the mobile operator.
MTN has 231 million subscribers in 22 countries across Africa, Asia and the Middle East. In September, the company was named as most admired brand in Africa in the Brand Africa 100 awards, beating Samsung, while it was also awarded the continent's most valuable brand - worth $4.6bn (£3bn).
MTN was South Africa's second mobile operator when it was set up in 1994 after the fall of apartheid. It began its expansion across Africa four years later with operations in Rwanda, Uganda and Swaziland.