Preliminary tests of a white powder discovered in a US Senate office building in Washington were positive for the potentially deadly poison ricin, police said.
Two out of three tests indicate ricin, US Capitol Police Chief Terrance Gainer said at a news conference.
The third test came out negative, and a fourth, more definitive test was under way, with results expected today.
Sixteen people who were near where the white powder was discovered in the mail were being decontaminated and would be allowed to go home, Mr Gainer said.
“At the moment we’re in a wait-and-see position from an analytical point of view in what next steps we may take,” he said.
That included what, if any decontamination of the Dirksen Senate Office Building would be needed.
Senate Majority Leader Bill Frist said no symptoms were reported by those near the powder. “
Everybody’s fine” and there is “no cause for alarm”, he said at the news conference.
“Nobody is sick, we don’t expect anybody to get sick,” said Mr Frist.
The powder was discovered at about 3pm local time yesterday in a mail room near Mr Frist’s office on the fourth floor of the Dirksen Building, police said.
A congressional official had said earlier that the powder was found in Mr Frist’s office suite.
Authorities do not know if the substance was found on a letter or a package, Mr Gainer said.
The US Homeland Security Department is monitoring the situation, spokesman Brian Roehrkasse said.
Ricin, derived from the castor bean plant, can kill within days. Twice as deadly as cobra venom, the poison is relatively easily made. It may be inhaled, ingested or injected.
Police found traces of ricin in a north London flat in January last year and arrested seven men of North African origin in connection with the virulent toxin that has been linked to al-Qaida terrorists and Iraq.
A package containing ricin was also found at a post facility serving Greenville-Spartanburg International Airport in South Carolina in October.
An FBI official said the bureau was awaiting the result of tests at the Fort Detrick laboratory in Maryland before deciding whether to more fully involved in the case.
Mail to congressional offices has been irradiated since deadly anthrax was found in letters sent to the offices of senators Tom Daschle and Patrick Leahy in 2001.
No one was arrested in those incidents.
Mr Frist said irradiation would probably have no effect on ricin because the substance is neither a virus or a bacterium.