WASHINGTON (AP) -- The FBI says the letters sent to President Barack Obama and Sen. Roger Wicker are related and are both postmarked out of Memphis, Tennessee, dated April 8.
In an intelligence bulletin obtained by The Associated Press, the FBI says the letters both say: "To see a wrong and not expose it, is to become a silent partner to its continuance." Both letters are signed, "I am KC and I approve this message."
The FBI says the substance in both letters have preliminarily tested positive for ricin, a potentially fatal poison.
Both the letters to Wicker, R-Miss., and to Obama were intercepted at off-site mail facilities.
The FBI says it is pursuing investigative leads to determine who sent the letters.
Check back for updates.
EARLIER STORY BELOW:
Preliminary testing indicates a letter addressed to President Barack Obama includes ricin, just a day after a letter addressed to a U.S. senator tested positive for the poison, federal officials said.
The letter is undergoing further testing because preliminary field tests can be unreliable, creating false positives.
The letter to Obama arrived Tuesday and was intercepted at a facility away from the White House, U.S. Secret Service spokesman Ed Donovan said.
Word of the letter comes a day after lawmakers revealed that a letter mailed to Sen. Roger Wicker tested positive for poisonous ricin. That letter to Wicker, a Republican, was intercepted at a Senate mail facility just outside Washington
Tensions have been high in Washington and across the country since the deadly bombings on Monday at the Boston Marathon that killed three people and injured more than 170.
The letter to Wicker, a Republican, was intercepted at a Senate mail facility just outside Washington and has tested positive for ricin. Sen. Claire McCaskill has said authorities have a suspect in mind in that case, though no one has been charged.
"The person that is a suspect writes a lot of letters to members," Sen. Claire McCaskill, D-Mo., said Tuesday as she emerged from a classified briefing.
Authorities declined to comment on a suspect or any other aspect of the investigation being led by Capitol Police and the FBI. The letter was intercepted at a Senate mail facility in Prince George's County, Md., just outside Washington, said Illinois Sen. Dick Durbin, a member of the Senate's Democratic leadership.