UPDATE: The White House letter has tested positive for ricin, but keep in mind false positives are common.
A letter addressed to President Obama containing a suspicious substance was intercepted Tuesday by authorities at a remote White House mail screening facility, according to the Secret Service.
The letter follows the discovery Tuesday of a ricin-laced letter sent to Sen. Roger Wicker (R-Miss.).
Edwin Donovan, deputy assistant director of the U.S. Secret Service, did not identify the substance. However, he said the Secret Service is working closely with the U.S. Capitol Police and the FBI.
The substance was detected at a facility run by the Secret Service, Donovan said.
Tensions are high because of the Boston bombing, but also because of upcoming votes on gun control and immigation this week.
Also breaking: The first floor of the Hart Senate building was evacuated over a suspicious package.
Senate police say they have a suspect in yesterday's ricin scare.
UPDATE: Sen. Carl Levin (D-MI) released a statement that a suspicious package was intercepted from his local Saginaw office.