Comcast is denying a report that it is blocking certain types of content with its bandwidth management technology, but that has done little to soothe concerns of net neutrality supporters.

An investigation by The Associated Press over the weekend claimed that Comcast blocks file-sharing to rein in bandwidth use for file transfers on peer-to-peer networks such as BitTorrent. The AP found that Comcast sends messages to people sending and receiving files telling them to stop communicating with each other, but the messages, or reset packets, appear to come from the users' computers.

The cable company on Monday sent out e-mails to media outlets pointing out that it manages traffic on its networks, which may be delayed by its bandwidth management technology, but it does not to block any applications.

"Comcast does not block access to any Web sites or online applications, including peer-to-peer services like BitTorrent," the company said in a statement to Reuters and The New York Times.

On Tuesday, several net neutrality groups who want legislation and accountability for telecommunications companies, chimed in on the debate.

Ben Scott, director of Free Press, a group that advocates network neutrality, said the revelation should serve as a warning.

"Comcast's BitTorrent blocking is the canary in the coal mine for net neutrality -- a clear example of an Internet service provider stifling innovation and free speech online," he said in a prepared statement. "Cable and phone companies like Comcast, AT&T, and Verizon should not be allowed to play gatekeeper over legal Internet content."

Comcast's practices seem to primarily affect file-sharing sites like BitTorrent, but they don't discriminate between pirated and original content, according to the AP. That means people trying to use such sites to distribute original work could be blocked from doing so. Comcast is an ISP and cable provider.

Scott added that the company should inform customers about bandwidth limitations rather than using fake IP addresses to send deceptive messages and block users' connections.

Markham Erickson, executive director and general counsel to the Open Internet Coalition, said that providers shouldn't act as "Internet gatekeepers" and make their own decisions about what Internet activities, files, or applications to filter.

"Without federal rules of the road to provide boundaries to prevent discriminatory behavior, consumers do not know whether the Comcast example is the whole of the problem or the tip of the iceberg," he said in a prepared statement. "What else is being blocked? What unilateral decisions are being made? Congress must act to answer these questions, protect consumers, and re-establish rules that preserve an open Internet."