By James Reynolds BBC Jerusalem correspondent

There is a simple logic to the security policy of Israeli carrier El Al - the greater the threat, the greater the precautions.

No other airline in the world runs such a great risk from hijack, sabotage or attack.

Its unique status has led it to develop a security strategy more extensive and robust than any other airline in the world.

El Al uses armed air marshals on all of its flights.

Plain clothes

The marshals are former combat soldiers from elite army units.

As part of their training they learn about small arms fire and hand-to-hand fighting.

They wear plain clothes and they sit among the passengers.

Only the crew is told who they are.

The air marshals sit near mirrors so they can keep an eye on what is going on behind them.

Pen knife

On occasions they have had to act.

Last month on a flight from Tel Aviv to Istanbul a passenger produced a pen knife.

He was quickly brought down by the air marshals who were on board.

Armed El Al guards have also had to act on the ground.

In July a man opened fire at an El Al counter at Los Angeles airport.

The man killed two people before he was shot dead by one of the airline's security guards at the airport.

The Israeli airline's special security measures are thought to cost millions of pounds a year.

But officials argue that the cost is well worth it.