MTN asks for 'leniency' on $5.2 billion Nigeria fine: source

South Africa's MTN has written to authorities in Nigeria asking for "leniency" and requesting a review of a $5.2 billion fine imposed on the telecoms provider for failing to cut off unregistered SIM card users, a regulatory source said on Tuesday. MTN sent a copy of the letter addressed to telecommunications regulator NCC to Nigeria's presidency, the source said, without providing specific details about the review.