FBI alerts police to ricin risk

US police have been made aware of the risks of ricin

The FBI has alerted police in the United States to the dangers of a deadly poison ricin after small amounts of the toxin were discovered in a London flat.

The use of ricin "would be most effective in an assassination by injection or as a food contaminant," the special edition of the FBI Intelligence Bulletin warned on Friday.

The toxin could also be used in a terrorist operation to contaminate closed ventilation systems, water supplies, lakes and rivers, said the FBI according to Reuters news agency.

Ricin comes from the seeds of the castor oil plant

British anti-terrorist officers are questioning seven people in connection with the ricin discovery in a north London flat this week.

Police have said six of the suspects are in their late teens, 20s and 30s and are of North African descent.

Only small traces of ricin were found but biochemical experts are attempting to determine if more poison could have been made at the flat and moved.

Made from the beans of the castor plant, the toxin is a naturally occurring chemical that can be manufactured easily.

UK Prime Minister Tony Blair said all the arrests showed the continued threat of international terrorism was "present and real and with us now and its potential is huge".

Ricin poison

Tiny amount can kill

No known antidote

Causes gastroenteritis, vomiting and seizures

More details on ricin poisoning

Security experts are trying to establish if the men have links to al-Qaeda.

Ricin is considered a potential bio-warfare or bio-terrorism agent and is on the United Kingdom's Centre for Disease Control and Prevention's "B" list of agents - meaning it is regarded as a moderate threat.

British health officials have urged doctors to look for signs of ricin poisoning, which include flu-like symptoms.

The most notable ricin death was the 1978 murder in London of the Bulgarian dissident Georgi Markov using a poison tipped umbrella.

Flashback: Dissident's poisoning
Click here for full Georgi Markov story

In the US several members of the Patriot's Council in Minnesota were convicted after manufacturing the poison in 1991, reported Reuters.