A central Florida man has been sentenced to seven years in prison for mailing a letter threatening to kill President Barack Obama and assaulting a U.S. Secret Service agent.

The U.S. attorney's office says in a news release that 24-year-old Jeremy Addison was sentenced Tuesday after pleading guilty last October.

Federal prosecutors say Addison sent the letter to the president in 2014 from the Volusia County Jail, where Addison was awaiting trial on an unrelated charge.

When a Secret Service agent tried to interview Addison, he spat in the agent's face. Prosecutors say he also told the agent he intended to kill him.

The judge increased Addison's punishment after he wrote another letter before sentencing, threatening to kill the federal prosecutor handling his case.