French authorities are trying to determine how a man who had explosive devices hidden inside his shoes managed to get through security checks and onto a flight for the United States.
The interior minister says airports in Paris have now increased security. Among the security measures are x-rays of all passengers' shoes.
The heavy security at Charles de Gaulle and Orly airports has been increased again. There are now more armed soldiers and police patrolling the concourses, and more bomb-sniffing dogs in use, some at check-in counters and passport control posts.
In Britain and at other European airports, security officials are on the alert for people trying to smuggle explosives in their shoes.
In France, questions are being asked about how a man, identified by the British passport he was carrying as Richard Reid, managed to get onto the American Airlines flight bound for Miami with explosives in his shoes.
He reportedly attempted to board the same flight the day before but was stopped because he was said to be acting suspiciously. After intense questioning he was given permission to board but missed the flight. He returned on Saturday.
There are reports that the passport, issued three weeks earlier in Brussels, may have been stolen. The French say they believe the man is actually Sri Lankan and is named Tariq Raja.
But for authorities here, the more urgent question is why screening devices at the airport failed to detect the plastic explosives and the detonator wires that apparently were fitted into the suspect's shoes.