(Adds comment from Interior Minister, paragraph 4)
MILAN, July 30 (Reuters) - A little-known leftist group said on Tuesday it placed incendiary devices at the offices of carmaker Fiat and a trade union on Monday, which raised fears of a return to political violence in Italy.
The Revolutionary Front for Communism (FR) sent the claim of responsibility to a Milan-based newspaper in an 11-page document spelling out its political position, police said.
Neither device went off, but the action prompted condemnation from officials in the wake of the assassination of a Labour Ministry advisor in March which was claimed by an offshoot of the Red Brigades, most active in Italy in the 1970s and 1980s.
Later on Tuesday, Interior Minister Giuseppe Pisanu said the FR group's claim of responsibility for the incendiary devices was credible and added that the Red Brigades appeared not to be connected to this incident.
The FR is believed to have been created in recent years and its initials were found at the site of an arson attack on a temporary labour agency in Milan in July last year.
Monday's devices were placed at the Milan headquarters of Fiat, which is in the process of laying off thousands of workers, and at the offices of labour union CISL -- the most centrist of Italy's three big union organisations -- near the city.