It is unclear how many viewers were affected by the clip, which lasted about 30 seconds, and featured full male nudity.

The clip showed a woman unzipping a man's trousers, followed by a graphic act between the two. It was from Club Jenna, an adult cable television channel.

The interruption happened just after the last touchdown by the Arizona Cardinals, who lost the match to the Pittsburgh Steelers.

Local media outlets reported that they received calls from furious viewers.

"I just figured it was another commercial until I looked up," viewer Cora King told the Arizona Daily Star.

"Then he did his little dance with everything hanging out."

The Super Bowl was being shown locally on Tucson-based KVOA-TV. The station sends its signals — both standard definition and high definition — to Cox Communcations, which then sends the signals to Comcast

KVOA-TV said it was "dismayed and disappointed" after some cable viewers had their match coverage disrupted towards the end of the game.

The company said the material was only seen by viewers of one cable network.

But Company President Gary Nielson told the BBC: "KVOA will investigate what happened and make sure our viewers get answers."

He added: "When the NBC feed of the Super Bowl was transmitted from KVOA to local cable providers and through over-the-air antennas, there was no pornographic material."

Comcast, the cable company whose viewers saw the material, said it was investigating.

Comcast is Southern Arizona's second-largest cable subscriber, with more than 80,000 customers in unincorporated Pima County, Marana and Oro Valley.