I don't think an applicant for citizenship needs to provide an FBI report or do any more than provide the initial documents. I only had to go to the federal police to have them take my fingerprints and now I'm waiting to pay for a notice in the local newspaper when they tell me to do so.
The initial documents required (in my case): copies of my DNI, a certificado de domicilio, a legalized copy of my birth certificate with the apostille and translation, and a certificate of my income by an Argentine accountant.