Internal Facebook documents released by a U.K. parliamentary committee offer the clearest evidence yet that the social network has used its enormous trove of user data as a competitive weapon, often in ways designed to keep its users in the dark.

Parliament's media committee accused Facebook on Wednesday of cutting special deals with some app developers to give them more access to data, while icing out others that it viewed as potential rivals.

In other documents, company executives discussed how they were keeping the company's collection and exploitation of user data from its users. That incl...