New York City Mayor Michael Bloomberg was threatened anonymously in two letters sent to Bloomberg's offices in Manhattan and Washington, D.C.

In addition to Bloomberg, another letter was sent to the director of the Mayors Against Illegal Guns in D.C. Browne said preliminary tests on that letter showed it also appeared to contain ricin, though the Washington police report of the incident said that "no hazmat (hazardous) material was found," said ABC News.

Bloomberg said "No, I do not feel threatened. This was not the first letter that was sent to anybody. In terms of why they did it - I don't know - the letter referred to our anti-gun efforts. There are 12,000 [people] that are going to be killed this year with guns and 19,000 are going to commit suicide by guns and we are not going to walk away from those efforts."

The poison, which comes from castor beans, stops cells from synthesizing proteins so victims can suffer organ failure.

Last month, ricin-tainted letters were sent to President Obama and to government offices, including that of Sen. Roger Wicker, R-Miss.