French police have said explosives found aboard a Royal Air Maroc plane were part of a failed bomb plot and not just a provocation.

Customs officials using sniffer dogs found the stick of explosives in between two passenger seats after the Boeing 747 had landed in eastern France on Wednesday night.

No suspects have yet been identified

Initial theories suggested the explosives - found without a detonator - might have been intended for clandestine onward delivery.

But investigators now believe it was an attempt at a bombing.

"This was done to make a hole in the plane," a judicial source told news agency Associated Press.

Mystery

Police are still at a loss as to who secreted the 100-gram stick of explosive, wrapped in aluminium, aboard the flight to Metz-Nancy airport from Marrakesh.

Investigations are still continuing into the 160 tourists and crew on board have found no one with any suspicious record.

Police from Strasbourg and French anti-terrorist and intelligence services have extended their search to include passengers on previous flights that day on the same plane.

Two theories

An early hypothesis was that the explosives could have been intended for delivery - placed aboard the plane during an internal flight and left there for transport during a subsequent international flight.

The same explosives were found in Richard Reid's shoes

But this theory now appears less likely, French sources said, because the risk to the courier was so much greater than that of using other means of transport.

Investigators are now tending towards the more sinister theory that a later passenger planned to attach a detonator to the explosives while aboard the plane's next scheduled flight back to Morocco.

Parliamentary elections taking place in Morocco on Friday could provide a motive for the plot.

'Shoe bomber's' choice

The explosive found was pentrite, a granular powder which can be used alone or in composition with other chemicals such as Semtex.

Semtex was used in the 1988 Lockerbie bombing which killed 270 people.

Pentrite is also the substance that was found in the shoes of Richard Reid, a British man who allegedly tried to blow up an airliner heading from Paris to Miami with a bomb in his shoes.