The figure also reveals one of the challenges Facebook may face as it expands worldwide, since the company has struggled to make as much money from mobile use as it has from desktops.

Thirty percent of new Facebook users in India register on a mobile phone, suggesting they don't also have an Internet-connected PC, Emily White, Facebook's director of mobile partnerships, said in a presentation at the Social Loco on Monday.

In its pre-IPO , Facebook reported that monthly active users in India more than doubled between from March 2011 to March 2012. The company indicated that India accounted for its third-fastest growing user base, at the same time its per-user revenue was falling.

Facebook has fewer users in Africa, but there too mobile usage is heavy. Nine out of 10 Facebook users in Africa use the social network from mobile devices, White said, though it wasn't clear if she meant exclusively or in addition to desktop use.

Its user base is growing quickly in some African countries. Last month it saw its user numbers in Mozambique grow by 18 percent, according to from Socialbakers.