WASHINGTON — The Federal Bureau of Investigation has collected information about religious, ethnic and national-origin characteristics of American communities, according to internal F.B.I. documents made public by the American Civil Liberties Union on Thursday. Citing the materials, the group urged the Justice Department to tighten restrictions on F.B.I. powers.

The documents show that in recent years, agents identified Arab-American and Muslim communities in Michigan as a potential terrorist recruitment ground; noted an increase in the African-American population of Georgia when analyzing “Black Separatist” groups; identified Chinese and Russian communities in San Francisco as a place to look for organized crime syndicates; and highlighted Latino communities as potentially harboring the Central American gang MS-13.

In a letter to Attorney General Eric H. Holder Jr., the A.C.L.U. asserted that the documents showed that “the F.B.I. is illegally and unconstitutionally” targeting people for investigation based on their race or religion. It asked Mr. Holder to bar agents from considering this kind of factor; current rules forbid the use of race or ethnicity unless describing a particular suspect, but contain a broad exception for national security or border-related investigations.

The F.B.I., however, said agents were doing their jobs by analyzing potential threats within their areas of responsibility. It said that the bureau was obeying rules barring investigative activity based “solely” on religion, race or ethnicity, but that such factors could help identify particular threats as well as potential victims.