Facebook Inc. is launching a new type of mobile advertising that targets consumers based on the apps they use, pushing the limits of how companies track what people do on their phones.

The social network is tracking the apps that people use through its popular Facebook Connect feature, which lets users log into millions of websites and apps as varied as Amazon.com, LinkedIn and Yelp with their Facebook identity. The company then targets ads based on that data, said people familiar with the company's plans.

Facebook may also track what people do on the apps, though it hasn't made a final decision, said one of the people.

The new ads could stoke privacy concerns because they let Facebook go a step further than mobile-ad networks, which track what ads people have clicked on through a phone's Web browser. Those networks aren't aware of all the apps that a user has on their phone.

Companies like Apple Inc. and Google Inc. track users' mobile apps but they approach ad targeting differently. Apple discloses to users in its privacy policy that it can target ads based on apps the person has downloaded from its App Store and iTunes. Google, however, doesn't target ads based on that data, though in theory it could. Neither Google nor Apple track what people do in their apps to target ads.