NEW YORK » Two threatening letters sent to Mayor Michael Bloomberg in New York and his gun-control group in Washington contained traces of the deadly poison ricin, police said today.

The anonymous letters 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 started by Bloomberg. Chief New York Police spokesman Paul Browne said preliminary testing indicted the presence of ricin in both letters but that more testing would be done.

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 some minor symptoms that have since abated, police said.

Both the letters contained threats to Bloomberg and an oily pinkish-orange substance, Browne said. He would not comment on what specific threats were made or where the letters were postmarked.

Word of the letters comes as a 37-year-old man is charged in Washington state with sending the toxin in letters to a federal judge, and about a month after letters containing the substance were addressed to President Barack Obama, a U.S. senator and a Mississippi judge. A Mississippi man was arrested in that case.

Police said the letter in Washington, D.C., was opened by Mark Glaze, the director of Mayors Against Illegal Guns. He was working out of a lobbying firm office.

A mayor’s spokesman also speaking for the nonprofit said he had no comment.

Federal officials were investigating. Browne would not say whether the letters were believed to be linked to any other recent ricin cases.

According to the Centers for Disease Control, ricin is a poison found naturally in castor beans. Symptoms can include difficulty breathing, vomiting and a redness on the skin depending on how the affected person comes into contact with the poison.