"The preparation of action has to be meticulous and studied in the smallest detail to inflict the maximum damage, above all to the economy," said a letter sent to the Il Tempo newspaper and signed by the Kommando Bestia, or Beast Command.
The group claimed to be a cell of the Anarchists Federation (FAI), which took responsibility for shooting the head of a nuclear company in the knee earlier this month.
Giorgio Piccirillo, head of Italy's secret service, on Wednesday giving testimony to a parliamentary committee warned of the return possible "spectacular actions" by the FAI and other domestic terror groups.
After a period of less activity, we can expect a gradual increase in attacks by the Informal Anarchist Federation," Piccirillo told the parliaments' constitutional affairs committee.
The previously unknown 'Olga' cell of the FAI said it shot in the leg Italian nuclear company Ansaldo's boss Roberto Adinolfi in the northwestern port city of Genoa earlier in May.
Extremist left and right-wing Italian terror groups in the 1970s and 1980s planted bombs and carried out political kidnappings. The Red Brigades carried abducted and killed former prime minister Aldo Moro in 1978