By Jonathan Stempel

(Reuters) - A Connecticut man already in custody after large quantities of firearms and ammunition were seized from his home was indicted on charges he made online threats to kill or injure Jews and other people, the U.S. Department of Justice said on Thursday.

Kendall Sullivan, 50, of Stamford, was charged on Wednesday by a federal grand jury in Bridgeport, Connecticut, with three counts of making threatening communications online, each punishable by up to five years in prison.

The defendant has been in custody since July 15, when he was charged in state court with unlawful possession of unregistered high-capacity magazines, the Justice Department said.

On the same day, FBI agents and Stamford police seized more than two dozen firearms, hundreds of rounds of ammunition and other firearm components from his home, the department added.

In an affidavit, an FBI agent said Sullivan told Stamford police in a videotaped interview that he made the threatening posts on the internet forum Metalthrone.net, with an intention "to verbally scare or frighten individuals or groups including Jews," but had no plan to carry out his threats.

A lawyer for Sullivan could not immediately be identified.

According to the indictment, Sullivan posted his threats between May 29 and July 5.

It alleged that Sullivan wrote that he had "a few 'Houses of Satan' in my Town," and that "if these Jews truly believe in their god Satan, I will upset their world. I will slaughter them and burn their Synagogue to the ground ... kids, goldfish, old folks."

The indictment also alleged that Sullivan wrote another forum user, whom he identified as Jewish, about his plan to meet at a Carvel ice cream store in Westport, where he would "shoot or run over you.... A 50 year old kills a Satanist with a 9mm."

The Stamford Police Department did not immediately respond to a request for additional comment.

The federal case is U.S. v. Sullivan, U.S. District Court, District of Connecticut.

(Reporting by Jonathan Stempel in New York; Editing by Dan Grebler)