Africa's biggest telecoms operator MTN Group on Monday reported a 72.3% tumble in full-year profit as a sharp devaluation in the Nigerian naira pushed its biggest unit MTN Nigeria to a loss.

South Africa-headquartered MTN said its headline earnings per share - one of the main profit measures - fell to 315 cents for the year ended on Dec. 31, from a restated 1,137 cents a year earlier.

Nigeria's central bank in June adopted new forex rules that MTN said had since led to an approximately 96.7% devaluation in the exchange rate to 907.1 naira per dollar by the end of December.

Adjusted headline earnings per share declined by 9.5% to 1,203 cents.

MTN, with 295 million customers in 19 African markets, declared a final divided of 330 cents per share and said its group service revenue grew by 6.9% to 210.1 billion rand ($11.09 billion). ($1 = 18.9519 rand) (Reporting by Nqobile Dludla; Edting by Tom Hogue and Muralikumar Anantharaman)