A bomb disposal team has just pulled up alongside a Pakistan Airways jet diverted to London's Stansted airport today after reports that a threat had been made to destroy the airliner.
Earlier, British fighter jets escorted the passenger plane to Stansted where police went on board and arrested two men on suspicion of endangering an aircraft.
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Passengers told Sky News in the UK that two men sitting at the back of the plane had repeatedly tried to gain access to the cockpit, but were prevented from doing so by crew. The men made threats to destroy the plane, the witnesses added.
The plane took off from the Pakistani city of Lahore. Pakistan is an ally of the US in the war on terror, but is also the source of virulent Islamic fundamentalism. The America government and its allies have alleged that Pakistan's intelligence service, the ISS, has elements that support Taliban activities in remote parts of Pakistan and neighboring Afghanistan.
Passengers left the plane and no one was hurt in the incident, a spokesman for the airport said.
Flight PK709 from Lahore in Pakistan had been due to land at Manchester in northern England with 297 passengers on board, but was diverted shortly before arrival.
Britain is on high alert after a soldier was hacked to death on a London street on Wednesday in what the government are treating as a terrorist incident.
A security source said early indications were that the plane was not the target of a terrorist attack.
A passenger who had just got off the plane told the BBC the pilot had informed passengers after landing that he had diverted to Stansted because of threats. The passenger, named by the BBC as Mr Munsif, said two men had been handcuffed on board and removed.
"We landed safely and then he announced that they had some kind of threat from someone and that's why he landed the plane," the passenger said, speaking by telephone.
"Essex Police have boarded a passenger plane diverted to Stansted Airport and two men have been arrested on suspicion of endangerment of an aircraft. They have been removed from the plane," the police said in a statement. The force is responsible for the area where Stansted is located.
"The two men arrested on suspicion of endangerment of an aircraft are aged 30 and 41. They are being taken to a police station for interview by detectives," the police added.
Stansted is one of London's less busy airports, preferred as a location for handling airplane security incidents. A spokesman for the airport said the plane was being held in an isolated area and that the rest of the airport was operating as normal.
Essex County Fire and Rescue Service said 10 fire engines had been sent to the airport.
The Pakistani plane was a Boeing 777, according to the flight tracking website www.flightradar.com.
According to two tracking websites, the aircraft broke off from its descent about 60 miles east of Manchester.
It turned and followed a wide arc over northeast England and out to the North Sea before heading towards London.
Britain launches military planes to intercept unidentified aircraft when they cannot be identified by other means, for example when the aircraft is not talking to air traffic controllers.
(Additional reporting by Brenda Goh, Kate Holton, Tim Hepher; writing by Estelle Shirbon; Editing by Kevin Liffey)