A US plane had to be diverted after a row broke out over one passenger's use of a device to prevent the seat in front of him from reclining.

A male and female passenger were involved in a heated dispute on Sunday, after the male passenger attached a Knee Defender to his seat, BBC reported.

The argument forced the United Airlines flight from Newark to Denver to make an unscheduled stop in Chicago.

Police investigated the incident but said it was a customer service issue.

The passengers involved were reported to be sitting in the Economy Plus section of the plane, which already provides an extra 10cm of leg room.

The fight began when the male passenger, seated in a middle seat of row 12, used the Knee Defender to stop the woman in front of him from reclining while he used his laptop, officials said, according to BBC.

A flight attendant asked him to remove the device - a small piece of plastic costing US$21.95 (S$27.40) which slots onto the tray table - but he refused.

The woman reacted by standing up, turning around and throwing a cup of water at him.

The flight crew then made the decision to divert the plane to Chicago, where police were waiting to meet it.

Under US law, the passengers, both 48, could have been fined for unruly behaviour.

But police decided the incident was not a threat to aviation security.

Despite this, the passengers were not allowed to continue onto Denver.

The US Federal Aviation Administration has said it is up to individual airlines to set rules about whether they allow the use of the Knee Defender on flights.

Most major US airlines, including United Airlines, have banned the device.

Its inventor, Ira Goldman, has said people should be courteous and tell the passenger sitting in front of them when they are using a Knee Defender.

"The Knee Defender says right on it: 'Be courteous. Do not hog space. Listen to the flight crew.' Apparently that is not what happened here," he told USA Today.