Anti-terrorism prosecutor Armando Spataro told The Associated Press on Tuesday that the two men _ a Libyan and an Egyptian _ were arrested overnight as suspected accomplices in Monday's bombing.
Police also found "a large quantity" of the same explosive used then. Sky Italia's TG24 TV says 100 kilograms (220 pounds) of the explosive were found, but Spataro would not confirm the amount.
Officials say the material is ammonia nitrate, an easily obtainable fertilizer ingredient.
A Libyan man on Monday exploded a bomb while trying to enter the barracks, seriously wounding himself. The motive is not known.