WASHINGTON - Federal regulators are looking into the interactions between Twitter and a company called Ubermedia, which develops applications that help users follow and communicate with each other on Twitter's popular online messaging service, according to two published reports.

The Federal Trade Commission inquiry is still at a preliminary stage and the focus remains unclear, the Wall Street Journal reported Thursday.

The Business Insider blog, which first reported the probe, said FTC antitrust investigators are studying how Twitter deals with outside companies that build applications for its messaging platform - such as photo-sharing, URL-shortening and advertising services - and whether it is trying to limit competition by buying or banning outside developers.

The FTC regularly looks into complaints - often filed by rivals - of anticompetitive behavior by companies in the technology sector. The initial probes do not always turn into full-blown investigations.

The Journal reported that Twitter blocked UberMedia from accessing messages on its platform, called "tweets," earlier this year, but has since restored access.

The FTC and Twitter declined comment. Ubermedia did not immediately respond to a request for comment.