PARIS (AFP) - Air France said Monday (Dec 21) it had taken legal action after the discovery of a fake bomb on board a flight from Mauritius to Paris that prompted an emergency landing in Kenya.

The airline "filed a legal complaint against unknown persons for endangering the life of others," a company spokesman said.

Separately, a police source said that a couple is being held in Paris over the fake bomb on the flight. They were reportedly taken into custody by border police on their return to France, a day after the flight was forced to make the landing.

A passenger alerted crew members to the item found inside a toilet cubicle on Sunday (Dec 20) on board a Boeing 777, which was carrying 459 passengers and 14 crew members from Mauritius to Paris.

The object, made up of cardboard, paper and a kitchen timer, was found to pose no danger to the aircraft or its passengers, Air France chief executive Frederic Gagey said on Sunday.

He said the "deduction" was that the item had been placed in a toilet cupboard by one of the passengers and said the bomb scare appeared to be the result of a "bad joke".

France is on high alert after militant attacks in Paris in November left 130 people dead, and is one of many countries taking extra security precautions.

Airlines are especially jittery after Islamic State militants, who claimed the Paris attacks, also said they were responsible for downing a Russian jet in Egypt in October after smuggling a bomb onto the plane, killing all 224 people on board.

Gagey said there had been three bomb scares on Air France planes in the United States in the past 15 days.