News outlets said the Federal Bureau of Investigation (FBI) confirmed the letter sent to Obama tested positive for the deadly poison ricin in preliminary analysis – the same chemical that was laced in a letter sent to Senator Roger Wicker earlier Wednesday.
Suspicious packages addressed to US Senator Jeff Flake were also intercepted in Phoenix prompting hazmat crews to appear on the scene, according to local authorities.
White House Press Secretary Jay Carney would not confirm or deny whether the suspicious letters and the Boston Marathon attacks are related, deferring to the FBI on several occasions.
"They have made a fairly clear statement," Carney said during the press conference. "I'm not going to assess it further from here."
Secret Service spokesman Edwin Donovan said the agency, which protects the president and his family, was working closely with the US Capitol Police and the Federal Bureau of Investigation to trace the origins of the letter.
The FBI said the letter to Obama “was immediately quarantined" by the authorities and found to contain ricin, according to Politico, while Reuters cited the following statement from the investigative body:
"The investigation into these letters remains ongoing, and more letters may still be received. There is no indication of a connection to the attack in Boston."
The Associated Press said the FBI believed the letter sent to Obama and one received by Sen. Roger Wicker are related, both of them sent from Memphis, Tennessee on April 8.
"To see a wrong and not expose it, is to become a silent partner to its continuance," the letter said, according to the FBI bulletin cited by AP, adding that both letters end: "I am KC and I approve this message."
Meanwhile, just blocks from the White House, Roll Call reported that "several suspicious packages" had appeared at the Senate office buildings Hart and Russell, citing an email sent to staffers that allegedly warned of “a suspicious envelope on the third floor of the Russell Senate Office Building.”
The White House confirmed on Wednesday that a suspicious letter had been to a senator, while MSNBC said Alabama Senator Richard Shelby, whose office is located on the third floor of the Russell Building, had also received a letter.
The area is being cleared by the authorities, and all mail to the US Senate has been put on temporary hold, said MSNBC.
Michigan Senator Carl Levin said his regional office Saginaw had also received a suspicious letter, according to the Associated Press.
"Earlier today, a staffer at my Saginaw regional office received a suspicious-looking letter," Levin said in a statement. "We do not know yet if the mail presented a threat," it said. It is not clear whether any of the developments are related to the bombings in Boston, and the White House would not comment on a possible link, citing ongoing investigations.