A bomb blast outside a high school in southern Italy that killed a 16-year-old student has stirred memories of the dark days decades ago when terrorists, anarchists and organized crime carried out dozens of bloody attacks.

Investigators had no firm clue on who was behind it and there was still no claim of responsibility Sunday, a day after the crude device made up of gas cylinders exploded outside a mainly all-girls vocational school in the Adriatic port town of Brindisi.

The student killed by the bomb was Melissa Bassi, known to her friends in Brindisi for her sunny smile and dream of becoming a fashion designer. Four other young women who were hospitalized with burns were reported Sunday to be improving.

The school is named after a judge killed alongside her husband, a famous anti-Mafia prosecutor, in a bombing in Palermo, Sicily, exactly 20 years ago, leading some to think the mob may be responsible.

Italy has been marking the 20th anniversary of the attack on the Sicilian highway that killed prosecutor Giovanni Falcone and his wife, but it was unclear if there was an organized crime link to Saturday's explosion.

Interior Minister Anna Maria Cancellieri, in charge of domestic security, said she was "struck" by the fact that the school was named after the slain hero and his wife, but she cautioned that investigators at that point "have no elements" to blame the school attack on organized crime.

The bombing follows a spate of recent attacks against Italian officials and government or public buildings by a group of anarchists, including the shooting and wounding of an official from a nuclear engineering firm, which is part of a state-controlled company. An anti-nuclear anarchist group that previously had targeted Italy's tax collection agency claimed responsibility for the shooting.

Authorities have said the Italian anarchists have worked in close contact with Greece-based anarchists. Brindisi is a major point of departure for ferries between Italy and Greece, but there was no immediate indication from investigators of any Greek link.

The attacks and threats lodged against authorities prompted the government on Friday to assign bodyguards to 550 individuals, and deploy 16,000 law enforcement officers nationwide.

"But you can't militarize the country," the interior minister said.

Italy coped with a severe terrorism outbreak in the 1970s and 1980s -- known as the "years of lead." In the worst attack, blamed on right-wing terrorists, 85 people were killed in a bomb blast at the Bologna train station in 1980. A Mafia terror campaign targeted churches and public buildings in Rome and Milan.

Corrriere della Sera, Italy's leading newspaper, said the government and investigators needed answers as soon as possible to avoid the country reliving the "fantasy of the strategy of tension."