The Johannesburg Stock Exchange (JSE) on Friday started an investigation into the timing of MTN Group’s announcement on Monday that the Nigerian Communications Commission (NCC) had fined them $5.2 billion.

“The investigation will follow due process to establish whether there have been any breaches of the listings requirements and can be a lengthy process,” said Andre Visser, head of Issuer Regulation at the JSE, in a statement on Friday.

“As with all price sensitive announcements, the Market Regulation team is looking into trades that took place before the announcement in order to determine if there is any evidence of possible insider trading,” added Peter Redman, a senior technical advisor in the Market Regulation division at the JSE.

MTN told shareholders on Monday that “the NCC has imposed a fine equivalent to $5.2bn on MTN Nigeria”.

“This fine relates to the timing of the disconnection of 5.1 million MTN Nigeria subscribers who were disconnected in August and September 2015 and is based on a fine of N200 000 for each unregistered subscriber,” said the company.

The announcement did not seem to have much impact on MTN’s share price, which was up 2.75% to R158.63 by 13:45 on Friday. MTN’s share price has dropped by 20% since Monday, taking over R60bn off its market value.

Fin24

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