NEW YORK (AP) -- A letter sent to the White House was similar to poison-laced missives mailed to New York Mayor Michael Bloomberg and to his gun-control group in Washington that contained threats about shooting people in the face, officials said Thursday.
The Secret Service said the letter addressed to President Barack Obama was intercepted by a White House mail screening facility, and it was turned over to the FBI's Joint Terrorism Task Force for testing and investigation.
Officials previously revealed that two threatening letters postmarked in Louisiana and sent to Bloomberg contained traces of the deadly poison ricin.
New York Police Department Commissioner Raymond Kelly said the letters apparently all came from the same machine. The letters sent to Bloomberg contained an oily pinkish-orange substance. It wasn't clear if the missive to Obama contained the same substance.
The body of the letter was addressed to "you" and referenced the gun law debate. Kelly said the letters say, in so many words: "Anyone who comes for my guns will be shot in the face." He refused to quote directly from the letters, saying he didn't want to do the author's bidding.
The billionaire mayor has emerged as one of the country's most potent gun-control advocates, able to press his case with both his public position and his private money.
The anonymous letters to Bloomberg were opened in New York on Friday at the city's mail facility in Manhattan and in Washington on Sunday at an office used by Mayors Against Illegal Guns, the nonprofit he started, police said Wednesday.
Testing indicated the presence of ricin in both letters. The postal workers' union, citing information it got in a Postal Service briefing, said the letters bore a Shreveport, La., postmark. Kelly would not comment on the origin of the letter.
Louisiana State Police spokeswoman Julie Lewis said state authorities have deferred to the FBI and have not opened an investigation. The Shreveport postal center handles mail from Louisiana, Texas and Arkansas, so the letter could have come from any of those states, Lewis said.
The people who initially came into contact with the letters showed no symptoms of exposure to the poison, but three officers who later examined the New York letter experienced minor symptoms that have since abated, police said.
Bloomberg didn't comment on Thursday. On Wednesday, he said he didn't know why they were sent.
One of the letters "obviously referred to our anti-gun efforts, but there's 12,000 people that are going to get killed this year with guns and 19,000 that are going to commit suicide with guns, and we're not going to walk away from those efforts," said Bloomberg, adding that he didn't feel threatened.
The letters were the latest in a string of toxin-laced missives, but authorities would not say whether the letters to Bloomberg and Obama were believed to be linked to any other recent case.
In Washington state, a 37-year-old was charged last week with threatening to kill a federal judge in a letter that contained ricin.
About a month earlier, letters containing the substance were addressed to Obama, a U.S. senator and a Mississippi judge. One of the letters postmarked in Memphis, Tenn., was traced back to Tupelo, Miss., and a Mississippi man was arrested.
According to the Centers for Disease Control and Prevention, ricin is a poison found naturally in castor beans. Symptoms can include difficulty breathing, vomiting and redness on the skin depending on how the affected person comes into contact with the poison.
Bloomberg and Boston Mayor Thomas Menino founded Mayors Against Illegal Guns, which now counts more than 700 mayors nationwide as members. It lobbies federal and state lawmakers, and it aired a spate of television ads this year urging Congress to expand background checks and pass other gun-control measures after the school shooting in Newtown, Conn. The background check proposal failed in a Senate vote in April, and other measures gun-control advocates wanted — including a ban on sales of military-style assault weapons — have stalled.
Separately, Bloomberg also has made political donations to candidates who share his desire for tougher gun restrictions. His super PAC, Independence USA, put $2.2 million into a Democratic primary this winter for a congressional seat in Illinois, for example. Bloomberg's choice, former state lawmaker Robin Kelly, won.
Associated Press Writer Jennifer Peltz in New York and Holbrook Mohr in Jackson, Miss., contributed to this report.