A man has been arrested after packages suspected to contain the poison ricin were sent to the Pentagon and President Trump.
William Clyde Allen III, from Logan, Utah, has been detained in connection with the suspicious parcels.
There were conflicting reports over whether the packages contained ricin or castor seeds, which can be used to make the poison.
At least two packages suspected of containing the poison were sent to the Pentagon this week.
The Pentagon’s mail screening facility on Monday had intercepted at least two packages, one addressed to defence secretary Jim Mattis and the other to navy chief admiral John Richardson.
Separately, the US secret service said it had obtained a “suspicious envelope” addressed to Mr Trump the same day.
“The envelope was not received at the White House, nor did it ever enter the White House,” the secret service said.
No one has been hurt.
Ricin is lethal even in small doses if swallowed, inhaled or injected.
It is 6,000 times more potent than cyanide, with no known antidote.