By Allan Little
BBC News, Paris
Plastic explosives were mistakenly loaded onto a plane at a Paris airport after security officials lost track of it during an exercise, police say.
The plastic explosives could be anywhere in the world, police say
Around 150 grams (about five ounces) of explosive were slipped into the bag of a passenger during sniffer dog training at Paris Charles de Gaulle airport.
The bag ended up on one of 90 flights leaving at the time, and police are now trying to track it down.
They stress the explosive is "no more dangerous than a bar of chocolate".
But airlines, airports and police forces around the world have been alerted.
It was a routine exercise that went wrong. An embarrassment but not, French police insist, dangerous.
The package of explosive was put in a bag at the airport on Friday to see if police dogs could detect it.
Someone though took their eye off the ball and the baggage handler unwittingly put the bag on a plane.
Police say they do not know which plane the bag ended up on; about 90 flights were leaving the airport at the time.
It could be on an internal flight in France, or be travelling as far away as the US, Japan and Brazil.
Resembles putty and can be moulded by hand
Best known is Semtex, designed in Czechoslovakia
Made for landmine clearance and industrial work
Was undetectable by dogs and airport security devices
Became popular with international terrorists
Police insist the package of explosives is no more harmful than a chocolate bar - it has no detonator and does not react to movement, shock or even fire.
But they do concede that somewhere in the world, one of the thousands of passengers who passed through the airport will get a nasty surprise when they open their luggage.