Nigeria’s telecoms watchdog imposed a NGN 1.04 trillion ($5.2 billion) fine on MTN Nigeria, the country’s largest operator, for failing to register the personal details of 5.1 million subscribers.

“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 NGN200, 000 for each unregistered subscriber,” MTN confirmed in a statement.

It added that it is in discussions with the Nigerian Communications Commission (NCC) to resolve the matter “in recognition of the circumstances that prevailed with regard to these subscribers”.

The NCC had asked all operators to register details of subscribers and deactivate those connections that were not registered.

It believed failure to do so “opened the country to grave security threats” according to Technology Times, who first broke the story, claiming this is “the biggest sanction ever witnessed in the Nigerian telecoms market.”

The fine was approved by Professor Umar Danbatta, NCC’s new chief.

A source told Technology Times that MTN Nigeria “disobeyed several directives issued to them”.

The report also said the matter was directed to the directorate of state security, the Nigerian army and the presidency, and this may not be the end of MTN’s troubles.

Though South Africa-based, Nigeria is MTN Group’s largest market, where it has 62.5 million subscribers followed by South Africa with 29 million subscribers.

Last week, in its Q3 results, the group said its total subscriber base had declined by 0.5 per cent over the last three months, as a result of losing the 5.1 million subscribers at the end of August. To date, 3.4 million of these subscribers have been reconnected.

It had noted at the time that “while management continues to engage with the regulator, performance continues to be impacted by ongoing regulatory restrictions.”