LONDON, England (CNN) — Counterterrorism police have foiled an apparent plot to launch a chemical attack in Britain, according to U.S. and British security sources.
The sources said the suspects had plans to lace a bomb with a chemical called osmium tetroxide.
The plot was to combine that chemical with explosives that could create a toxic cloud on detonation, the sources said.
Police suspect such a device could have been used to target a shopping center, an airport terminal, a nightclub, or a crowded city center.
There is no suggestion by police sources that any osmium tetroxide was found in possession of the suspects, or that they had managed to obtain any.
Tuesday afternoon, a spokesman at Scotland Yard said investigators were not prepared to discuss the alleged plot.
Chemical experts said osmium tetroxide is toxic, openly available, and used primarily in research laboratories. It can give off a vapor that would cause skin and eye irritation. In confined spaces it can be lethal.
This is the first time osmium tetroxide has been associated with an alleged terrorist plot.
Scotland Yard would not say whether the alleged chemical plot is connected to arrests made last week by British counterterrorism forces.
British police have been given more time to question nine men being held under the Terrorism Act of 2000. They were arrested last week, and police recovered half a ton of the fertilizer, which can be used as an explosive.
Tuesday, one of the nine, a 17-year-old, was charged with conspiracy to cause explosions with intent to injure or damage property.
A lawyer for three of the detainees declined to comment.
Two other men were arrested in Canada and Saudi Arabia.
The Royal Canadian Mounted Police have issued a statement acknowledging that the arrest of a 24-year-old computer software designer in Ottawa is linked to the British arrests.