Nigeria had 15 million active Facebook users as of June 30 this year, the giant social network said in statistics published today.

South Africa has 12 million monthly active  users, the data showed and  Kenya 4.5 million.

Majority  of the users logged on the service using  mobile devices to access their profiles. Facebook said.

Facebook opened its first African office in Johannesburg in June as the continent’s growing population and relatively low levels of internet access present a large untapped market for the social network to earn advertising revenue.

Facebook says with its strong advertising partnerships in Africa it would use the new office in Johannesburg to expand its business across the continent.

The numbers, the first Facebook has published for Nigeria, Africa’s most populous nation and Kenya, East Africa’s most developed, show the two nations as important entry points on a continent of nearly one billion people.

“Mobile is not a trend; it’s the fastest adoption of disruptive technology in history of communication,” said Nunu Ntshingila, Facebook’s head of Africa, in a statement.

Facebook said its active user population in Africa grew 20 percent to 120 million in June from 100 million in September last year. A large portion of these users were in North Africa.