UPDATE 2-S.Africa's MTN wary about growth in Nigeria

* Earnings up 9 pct

* Data revenue up 33 pct

* Expects to add 17.5 mln users in 2015 (Recasts with quotes)

JOHANNESBURG, March 4 (Reuters) - Africa’s largest telecoms provider MTN Group reported muted full-year earnings growth and warned of possible headwinds as weaker oil prices bring economic doubts to its biggest market in Nigeria.

The west African country contributed nearly 37 percent of MTN’s total revenue, while its South African home market made up about 27 percent.

“In Nigeria some level of uncertainty remains with regards to the implications of the oil price and currency fluctuations, which may lead to slower economic growth,” MTN said in a statement.

Authorities in Africa’s biggest economy have devalued the naira currency and raided foreign exchange reserves to feed demand following the slump in crude prices.

A tough regulatory environment has also meant MTN has been forced to offer similar tariffs to its own subscribers and those of its smaller rivals. It has also been hit with bans against selling SIM cards and promotional pricing.

“It would appear that the regulatory pressure may ease, but the unknown at this stage is the economic impact of the falling oil price,” said Reuben Beelders, portfolio manager at Gryphon Asset Management.

MTN, which has operations in nearly two dozen countries across Africa and the Middle East, said it would invest nearly 80 percent more capital in South Africa in 2015. This, analysts said, was to keep up with rival Vodacom’s expansion.

Nigeria’s capital spend will increase by 5 percent although it is expected to contribute more than a quarter of the 17.5 million new subscribers MTN hopes to sign on this year.

MTN surprised investors by declaring a 1,245 cents per share total dividend, up from 1,035 cents last year. It said it planned increases of between 5-15 percent a year, which sent the shares up as much as 2.8 percent.

One analyst said he was concerned that the firm might not be able to meet that goal.

“When one looks at MTN right now, how certain is the dividend and dividend growth going forward?” said Nadim Mohammed, an analyst at First Avenue Investment Management.

MTN’s diluted headline earnings per share, the main measure of profitability in South Africa, rose to 1,527 cents in the year ended December, up nearly 9 percent from a year ago. Data was a key growth driver, climbing 33 percent to contribute nearly a fifth of overall revenue.

$1 = 11.75 rand Editing by Elaine Hardcastle