Ricin was found in a London flat in January
France's interior minister has said that traces of the poison ricin discovered in a Paris railway station could be linked to a terrorist network with Chechen connections.
Nicolas Sarkozy said there was no proof that a ricin attack was being planned against France, but he said there was a possible connection with several men arrested last December for allegedly planning to attack the Russian embassy in Paris.
Two vials of the potentially deadly substance were found inside a locker at the Gare de Lyon, according to ministry officials.
Mr Sarkozy told French radio that the quantities of the substance were "non-lethal", although they were found with ethanol and acetone.
"A mixture of the three can make an extremely nasty poison," he said.
Ricin, a toxin found in castor beans, can be fatal when inhaled or ingested.
The substance is 6,000 times more powerful than cyanide and has been used in the past as a bio-weapon.
Two more people were detained in France for alleged links with the pro-Chechen terrorist network on Tuesday, though there has been no indication that this was connected with the ricin discovery.
The group had planned the embassy attack to avenge the deaths of Islamists in Chechnya and in the Moscow theatre siege last October.
Ricin is found naturally in castor beans
French police have said that the nine men arrested, who were all of North African origin, had been trained in Chechen rebel camps in Georgia's Pankisi Gorge and may have been in contact with senior figures in al-Qaeda.
One of the men was the brother of a French national being held at the US base at Guantanamo Bay, Cuba.
The Paris discovery was made on Monday by French police, after they received a telephone call from the state railway company SNCF, according to the French news agency AFP.
The announcement of the find came as the French authorities heightened security against terrorist targets following the launch of a US-led military strike against Iraq.
France has already doubled the number of soldiers in its streets, and ordered increased surveillance of train stations, ports and other sensitive areas.
Ricin is on America's Center for Disease Control and Prevention's B list of bio-warfare agents, and is therefore classed as a moderate threat.
The poison first came to the attention of bio-warfare experts in 1978, when Bulgarian dissident Georgi Markov was killed by secret agents in London who used a ricin-laced pellet fired from the tip of an umbrella.
In January, police in the UK discovered a stash of ricin during a raid on a flat in London.
Three men were charged with plotting
to produce chemical weapons in relation to the incident.