An Egyptair flight en route from Cairo to New York has been forced to land at Glasgow Prestwick Airport after a passenger found a note in the toilet saying: "I will set this plane on fire".
Typhoon fighter jets were scrambled to escort the plane as it landed at the airport at 2.20pm BST.
Passenger Nada Tawfik, a journalist who was travelling on the flight with her three-year-old daughter, said she found the note, which had been written in pencil on a paper napkin and left in the toilet.
"I found the note when I went to the restroom, and immediately went to the plane crew and told them," Tawfik said.
"It was written on a hard napkin, in pencil, and the pencil was still there by the note, in the restroom.
"I said to the cabin crew, make sure you keep the pencil, as there may be fingerprints. It appeared to be written in a child's handwriting."
Tawfik spoke from on board the plane, which was being held on a remote runway at the airport.
"We're still here on the plane," Tawfik added. "As you can imagine it is a pretty tense situation. Everyone is concerned."
Air traffic controllers at Prestwick confirmed action was taken following an unspecified "problem", though they did not elaborate.
Standard procedure was being followed, they said.
Police Scotland confirmed an incident at the airport was ongoing, and said officers were at the scene.
The number of passengers on board the plane has not been confirmed, though the plane has the capacity to seat 400.
Eyewitnesses said the plane landed at a remote runway at the airport in Ayrshire, Scotland.
Passengers and crew are being kept on board, according to reports. Armed police were in attendance and roads leading to the airport were closed due to the ongoing incident.
One driver reported seeing five police cars, fire engines, and ambulances travelling southbound on the A77, apparently heading for the airport.
A Prestwick Airport spokesman said he could not discuss the nature of the incident.
"The (diverted) plane was on route from Cairo to JFK in New York. It is safely on the tarmac at Prestwick," said the spokesman.
"The airport is open for business with flights arriving and taking off. The police are involved and on the scene. They have the lead in this."
The spokesman added that all flights at the airport were operating as normal. Train and bus services between Glasgow and Prestwick have been suspended.