Three of the world’s biggest airlines have admitted some of their planes have cameras installed on the backs of passenger seats.

American Airlines, United Airlines and Singapore Airlines have new seat-back entertainment systems that include cameras.

They could also be on planes used by other carriers.

Companies that make the entertainment systems are fitting them with cameras to offer passengers options such as seat-to-seat video conferencing, according to an American Airlines spokesman.

But American, United and Singapore all say they have never activated the cameras and have no plans to use them.

A passenger on a Singapore flight tweeted a photograph last week of the seat-back display, prompting other air travellers to voice concerns about their privacy at 30,000ft.

Vitaly Kamluk, who photographed the camera on his flight, suggested that carriers should cover the lenses with stickers and said it would be easy for airlines to monitor passengers with them.

Just found this interesting sensor looking at me from the seat back on board of Singapore Airlines. Any expert opinion of whether this a camera? Perhaps @SingaporeAir could clarify how it is used? pic.twitter.com/vy0usqruZG — Vitaly Kamluk (@vkamluk) February 17, 2019

“The cameras are probably not used now,” he tweeted. “But if they are wired, operational, bundled with mic, it’s a matter of one smart hack to use them on 84+ aircrafts and spy on passengers.”

American Airlines spokesman Ross Feinstein said cameras were in “premium economy” seats on 82 Boeing 777 and Airbus A330-200 jets.

“Cameras are a standard feature on many in-flight entertainment systems used by multiple airlines,” he said.

British Airways told The Independent none of its planes had cameras on seat backs.

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Singapore spokesman James Boyd said cameras were on 84 Airbus A350s, Airbus A380s and Boeing 777s and 787s.

But a United spokeswoman repeatedly told reporters on Friday that none of its entertainment systems had cameras – before apologising and saying that some did.

Delta did not respond to questions about some of its entertainment systems, which appear to be identical to those on American and United.

The airlines stressed that they did not add the cameras – saying manufacturers embedded them in the entertainment systems.

American’s systems are made by Panasonic, while Singapore uses Panasonic and Thales, according to airline representatives. Neither Panasonic nor Thales responded immediately to requests to comment.

Additional reporting by AP