US intercepts 'ricin' letter to Obama

A letter addressed to US President Barack Obama containing a "suspicious substance" has been intercepted.
Initial tests on the letter, identified at a remote facility, showed the presence of the lethal toxin ricin.
The US Secret Service said the letter arrived at the facility on 16 April, the same day a letter intended for a US senator tested positive for ricin.
Meanwhile, US Capitol Police are questioning a suspect in connection with the tainted letters, reports say.
In a separate development, areas within two senate office buildings have been cleared over suspicious letters.
The letter addressed to the president has tested positive for ricin, according to US media reports, but the contents are being sent to an accredited laboratory for further analysis, as the preliminary results need further verification.
All congressional mail has been sorted and tested off-site since anthrax was posted to two senators in 2001.


Ricin
Can be fatal when inhaled, ingested or - most dangerously - injected
One to three castor beans chewed by a child, or just eight seeds chewed by an adult, can be fatal
The toxin is part of the waste produced when castor oil is made
Q&A: What is ricin?
A spokesman for the Secret Service, which protects the US president and his family, said it was liaising with the US Capitol Police and Federal Bureau of Investigation (FBI) to trace the origins of the letter.
"This facility routinely identifies letters or parcels that require secondary screening or scientific testing before delivery," Edwin Donovan said.
The letter intercepted on Tuesday was intended for Roger Wicker, a Republican senator representing Mississippi.
Ricin, extracted from castor beans, is 1,000 times more toxic than cyanide.
It can be fatal when inhaled, swallowed or injected, although it is possible to recover from exposure.
Correspondents say there is a heightened sense of alert in the capital after the deadly bomb attacks at the Boston marathon but there is no indication so far of any connection between the two incidents.