Four people were being questioned Sunday over a suspicious device that was found in the restroom of an Air France flight, prompting an emergency landing in Kenya early in the day.

The four had all been on board Air France Flight 463, a Boeing 777 bound from Mauritius to Paris, which was diverted to the coastal Kenyan city of Mombasa after the device was found, Kenyan Cabinet secretary for the Ministry of Interior Joseph Nkaissery told CNN. He did not disclose their nationalities.

The object was analyzed and found to contain no explosives, the airline said.

Air France CEO Frederic Gagey described the object at a press conference Sunday afternoon as a cardboard box containing papers, with “something like a kitchen timer” inside it.

It was found by a passenger in a cupboard behind the restroom mirror, he said. He could not say if the object was assembled before the flight, but the materials were not ones that would usually be on board the aircraft.

He said an inquiry must be carried out to determine who planted the item in the restroom, an act he described as “stupid” and “completely unacceptable.”

“It seems like a nasty joke,” he said. “This is behavior which is in extremely bad taste.”

Gagey said the 473 stranded passengers and crew, who had been evacuated from the aircraft by slides, then accommodated at a hotel in Mombasa, would travel on to France in the next few hours.

There had been no security failure by Mauritian airport authorities, as the item contained no explosives and was not something that would be picked up in screening.

Nevertheless, the airline said in a statement that it was reinforcing security measures in Mauritius.

The airline paid tribute to the efficiency and professionalism of its crew.

The flight, which was destined for Charles de Gaulle airport in Paris, requested permission to land at Moi International Airport in Mombasa after the device was discovered in the restroom, Kenyan police chief Joseph Boinnet said.

“The plane landed there safely at 12:37 a.m. local time,” Boinnet said in a statement.

Kenyan investigators were working in liaison with France and Mauritius, Kenya’s Interior Ministry tweeted.

The Kenyan Interior Ministry tweeted that the passengers and 14 crew members had all been safely relocated to hotels.

It tweeted pictures of the passengers eating lunch at a hotel and being briefed by Kenyan officials in a meeting room.

The airport was temporarily shut down following the incident, but has since reopened, according to the Kenya Airports Authority.

The island nation of Mauritius sits in the turquoise waters of the Indian Ocean and is a popular tourist destination known for its pristine beaches.

Mombasa, which is along the Indian Ocean, is the second-largest city in Kenya.