The letter contained "a granular substance that preliminarily tested positive for ricin," said an FBI statement. But the statement added: "There is no indication of a connection to the attack in Boston," where three people were killed in bombings at the Boston Marathon on Monday.

A letter addressed to U.S. President Barack Obama contained a substance that preliminarily tested positive for the deadly poison ricin, authorities said on Wednesday.

News that the letter to Mr. Obama was being investigated came as a flurry of other reports of suspicious letters and a package caused the evacuation of parts of two Senate buildings and set nerves in Washington on edge.

The letter contained “a granular substance that preliminarily tested positive for ricin,” said an FBI statement. But the statement added: “There is no indication of a connection to the attack in Boston,” where three people were killed in bombings at the Boston Marathon on Monday.

The U.S. Secret Service said the letter was received at a mail screening facility on Tuesday.

The mail facility that received the letter was not located near the White House itself, it said.

“The Secret Service is working closely with the U.S. Capitol Police and the FBI in this investigation,” it said.

Parts of the Russell and Hart Senate office buildings were cleared while officials investigated suspicious letters and a package, said a Capitol Police spokesman.

CNN read a statement from a spokesman to Senator Richard Shelby, saying that Capitol Police were investigating a suspicious package that had been delivered to their office.

Keywords: Obama mailricin

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