AMBAZAC, France -- The explosion on a Paris-Toulouse express train that killed five passengers and injured 27 was caused by a powerful bomb, 'intentionally planted,' experts said Tuesday.
In Paris, Interior Minister Gaston Defferre immediately tightened security on trains and in rail stations, ordering the same sort of strict checks for rail passengers that air travelers undergo.
Police bomb expert Claude Calisti said the blast in the baggage compartment of Capitole Express Monday evening was caused by 'several pounds of extremely powerful explosives, intentionally planted.'
Defferre said the number of police in major stations will be increased, passenger baggage will be searched and passengers will be asked to go through a metal detector.
Calisti, discounting an accident, said a 'dry' type of plastic explosive with an electric detonator had been used.
'Terrorists clandestinely transporting explosives are usually sufficiently knowledgeable that they take the necessary precautions to avoid an explosion -- they keep the explosive and its detonator in separate packets,' he said.
Police said investigators were exploring the possibility the attack - which remained unclaimed 24 hours later -- was the work of an extremist right-wing group.
Investigators refused to speculate on whether the international terrorist Carlos could have been responsible for the attack. The Venezuelan-born mastermind had threatened attacks against France in reprisal for the arrest of two fellow terrorists.
Investigators credited the engineer of the southern Toulouse-bound train for averting a greater tragedy by stopping the train, which was traveling between 85 and 100 mph when the bomb exploded.
'If the train engineer had failed to bring the train to a halt and the train had derailed, it would have been a major disaster,' one investigator said.
The blast went off shortly before 2 p.m. EST as the electric train was nearing the central French village of Ambazac on its way to Toulouse.
Carlos was immediately suspected because the explosion coincided with the expiration of a month-long period he gave to the French government to release Magdalena Kaupp and Bruno Breguet, respectively West German and Swiss terrorists held in a Paris jail.
In a letter forwarded via the French embassy in Holland, Carlos said that failure to bow to his ultimatum would prompt him to 'act' against France.
Wanted in Paris for the shooting of two police officers, and the bombing of a drugstore, Carlos is also accused of the 1975 raid on OPEC headquarters in Vienna in which three persons were killed.
None of the victims of the blast had a criminal record, police said, ruling out any possibility that the explosives had been carried by one of the dead passengers. Among the dead was the sister of former Finance Minister Jean-Pierre Fourcade.
A woman passenger told investigators that shortly before the explosion, she saw a young man walking rapidly through the coach aisle in a state of apparent agitation.