Nigeria's communications regulator says it will not buckle to pressure from MTN shareholders to reduce a $5.2 billion fine meted out to the South African-based telecommunications giant.

Spokesman Tony Ojobo of the Nigerian Communications Commission told The Associated Press on Thursday that MTN Nigeria is in breach of a slew of regulations with 28 infractions.

The fine is for MTN failing to meet a deadline to deactivate 5.2 million unregistered cellphone SIM cards — considered a security threat as Nigeria fights an Islamic uprising and rampant kidnappings and armed robberies.

Ojobo was responding to charges from MTN shareholders that the fine is punitive. He said Nigeria's four cellphone service providers signed an agreement that set the fines in 2011 and MTN was the only company not to comply.