The explosion near the Arc de Triomphe during yesterday evening's rush hour - the second attack close to a Paris landmark in a month - will prompt questions about the effectiveness of security measures taken since the first attack.
Several thousand people a day have been stopped and asked for identity papers in Paris and other big French cities since the bombing of Saint- Michel Metro station, near the cathedral of Notre Dame last month. But no one has been held in connection with the explosion.
Automatic left-luggage lockers at mainline railway stations were closed, and notices went up in public places instructing people not to leave bags unattended. Litter bins on the platforms of railway and Metro stations were sealed, and some big stores and galleries introduced their own security checks. Litter bins on main thoroughfares, however, were left in place unsealed, and it was in one of these that yesterday's bomb was planted.
While hoping that the latest attack could provide clues to the first bombing, anti-terrorist officers cautioned against making an automatic link between the two. They noted that a different group could have been responsible, trying to use the cover of the first bomb to mislead investigators.
Although the Saint-Michel bomb is now generally accepted to have been the work of Algerian fundamentalist terrorists, the possibility of a Basque connection with yesterday's bomb cannot be excluded.
It has been widely reported that it was French police who tracked a Basque terrorist cell plotting an attack on King Juan Carlos of Spain in Majorca and that it was on the basis of their intelligence that members of the group were rounded up last week.
The only tangible and publicised progress in the Saint-Michel investigation has been the identification by Algerian intelligence services of one of three photofit pictures of "important witnesses" issued by French police.
The identification of the man as a member of the Armed Islamic Group (GIA), one of the most ruthless Algerian terrorist organisations and the one that carried out the hijacking of the Air France plane last Christmas, seemed to establish an Algerian link beyond any doubt.
The type of bomb - explosives pressed into a camping gas cylinder - was characteristic of Algerian terrorist groups. However, none of the three claims of responsibility - all from Algerian groups and two from the GIA - has been authenticated.