The feds have arrested an alleged neo-Nazi and have charged him with leaving anti-Semitic and threatening messages with an unnamed Jewish organization in Manhattan, according to a criminal complaint unsealed on Tuesday.

Authorities allege that Garrett Kelsey, 31, of Cedar Rapids, Iowa, called a New York-based Jewish organization in May and left a threatening voicemail laced with anti-Semitic vitriol — then followed up with an email demanding that the organization take down a video it posted about Nordic neo-Nazi groups, court papers state.

“My people have f—ing slaughtered your f—ing people before and we will do it again,” Garrett said in the voicemail, according to a criminal complaint filed against him in Manhattan federal court. “And right now, you are giving us incentive to do that . . . . Filthy f—ing Jews.”

A day after making the communiques, Kelsey took part in a voluntary interview with law enforcement in which he admitted to leaving the messages — and a week later he changed his Facebook cover photo to a World War II-era image of Jewish residents from a ghetto in Warsaw, Poland, lined up against a wall with their hands up.

Kelsey was arrested on Tuesday morning and has been charged with one count of transmitting threats to injure a person across state lines, which carries a maximum sentence of five years in prison. He could not be reached for comment.