Facebook CTO Bret Taylor said at the Inside Social Apps conference that mobile was the "primary focus" of its social network this year. He noted that the phone was the fastest-growing segment and that those who used it were twice as active as those on the desktop. Additions from last year, such as single sign-on, were put in place to make Facebook-aware apps easier, he told Insider Facebook.

"Mobile is inherently social," Taylor said, noting that a phone by definition was a communication device.

He didn't give clues but said he expected to see innovative apps with "really fluid integration" of Facebook.

The company has already started on the project as it confirmed that it had bought Rel8tion for its first mobile ad effort. While the intentions aren't known, the fledgling startup is known to have been preparing an ad system that targets the elements of social networks, such as basic demographics as well as education, a current job or relationship status.

Its entry would put it into further competition with Google by pitting Facebook mobile ads against AdMob and could provide some less direct competition with Apple's iAds. The system is unlikely to develop into a fully independent mobile ad platform and could be limited to both official apps and those that use a Facebook tie-in.

Facebook wouldn't confirm its goals in a response to AllThingsD but did say the startup, led by former Microsoft executives Peter Wilson and Scott Hannan, would join Facebook's Seattle office.

The site has been making increasing pushes into mobile but is still relatively limited. Some platforms tie parts of Facebook into the OS, such as webOS and Windows Phone 7, but most are limited to stand-alone apps. The largest initiative from the Palo Alto firm was Places, which virtually depends on mobile for its location-based check-ins and sharing for Android and iPhone.