The anthrax scare gripping the United States has widened further with traces of the germ warfare agent being detected at a mail inspection centre serving the US Supreme Court.
The germ has also been discovered in the offices of three members of the House of Representatives and at a CIA facility.
In other developments, authorities held out the possibility that there was at least one more anthrax-tainted letter somewhere in Washington and weighed giving anthrax vaccines to decontamination personnel and others.
White House spokesman Mr Ari Fleischer said investigators had determined that the pure, concentrated and highly dangerous anthrax delivered in a letter last week to Senate majority leader Mr Tom Daschle "could be produced by a PhD microbiologist and a sophisticated laboratory."
"That does not rule out that it could be state-sponsored," Mr Fleischer said at a briefing.
There could be as many as forty places in the US with the ability to produce the lethal version of anthrax that was mailed to Mr Daschle, said Senator Bob Graham, Senate intelligence committee chairman.
"Most of them are associated with a university, a medical centre or a veterinary centre," Mr Graham, a Florida democrat said.
"But I don't believe any source of this has either been ruled in or ruled out, sources within the United States or elsewhere," he added.