A letter addressed to U.S. Republican Senator Roger Wicker of Mississippi tested positive for the deadly poison ricin on Tuesday.<br/> <br />The letter was post marked from Memphis, Tennessee, but had no return address. It was intercepted by authorities before it reached the Senator's office.<br/> <br />Senator Jeff Flake said the incident is cause for alarm.<br/> <br />(SOUNDBITE) (English) SENATOR JEFF FLAKE, REPUBLICAN FROM ARIZONA, SAYING:<br/> <br />"Obviously that's concerning. You know it's not just members concerned. Rarely does it get to the member before it goes through a lot of staff. That's a big concern obviously for all of us. So we're very anxious to get more details."<br/> <br />Officials say all mail to the Senate has been stopped for the time being.<br/> <br />Ricin is a lethal poison found naturally in castor beans.
