New York: Two letters addressed to New York City Mayor Michael Bloomberg and his gun control group contained material believed to be the deadly poison ricin, and referenced the debate on gun laws, police said on Wednesday. The New York Police Department said initial tests on the two letters, opened in New York and Washington, DC, indicated the presence of ricin. Emergency workers who came in contact with the letters showed minor symptoms of ricin exposure, the police said. One of the letters was opened on Sunday in Washington by Mark Glaze, the director of Mayors Against Illegal Guns, a group that lobbies for stricter gun laws and was founded by Bloomberg. The other letter was opened on Friday at a mail facility in Manhattan. Both contained threats against Mr Bloomberg and mentioned the gun debate, police said in a statement.