Anthrax has been discovered at the US Supreme Court mail sorting office, according to reports.
This latest case comes in the wake of the discovery of anthrax at a CIA mail sorting office.
Test results have confirmed there was a "trace amount" of anthrax in the CIA mailroom, a spokesman said today.
"I'm told that the amount is considered medically insignificant. We took the step of closing that building for testing and cleaning," he said.
Three people have died this month and at least 11 others have infections of the rare disease in a spate of cases along the East Coast involving attacks with anthrax-laced letters.
The anthrax threat has also touched the White House, Congress and the State Department.
The CIA mail office is on the CIA compound in Langley, Virginia, but is separate from the agency's main headquarters.
Authorities said late yesterday a 59-year-old man who worked at a State Department mail-sorting office in the Washington suburb of Sterling, Virginia, contracted inhalation anthrax - the most deadly form of the disease.
The State Department said the Virginia office receives mail from the Brentwood central mail-processing office in Washington. Two employees from the Brentwood centre died earlier this week and others have contracted inhalational anthrax.
Two more anthrax-contaminated spots were also found yesterday in a US Senate office where an anthrax-laced letter was opened in Senate Majority Leader Mr Tom Daschle's office on October 15th.