Early tests have indicated that a white powder found in a US Senate office building yesterday was the deadly poison ricin.
A suspicious powder was also found at a postal facility in Wallingford, Connecticut, where anthrax spores were found in the 2001 anthrax-mailings, which killed five people in different parts of the eastern United States.
No illnesses have been reported relating to yesterday's incidents.
Preliminary tests showed the substance found in a Senate mail handling room yesterday was ricin and a federal law-enforcement official said definitive testing results from the US army's Fort Detrick were expected this afternoon.
US security services are on alert for possible attacks in America by extremists as President George W. Bush pursues a war on terrorism, but there was no immediate indication who was behind this incident.
Several airlines cancelled flights to the United States, including to Washington, over the weekend due to security concerns.