More on that detection of radioactive particles on the US west coast.
Reuters say two "diplomatic sources" tell them "miniscule amounts" have been detected - at a level far too low to cause any harm to humans.
One diplomat, citing information from a network of international monitoring stations, described the
material as "ever so slight", consisting of only a few particles. "They are irrelevant," the diplomat added.
Another diplomatic source also said the level was "very low".
The Vienna-based Comprehensive Test Ban Treaty Organisation, an independent body for monitoring possible breaches of the test ban, has more than 60 stations around the world, including one in Sacramento in California.
They can pick up very small amounts of radioactive particles such as iodine isotopes.
"Even a single radioactive atom can cause them to measure something and this is more or less what we have seen in the Sacramento station," said the first diplomat, who declined to be named.
Asked if they were believed to originate from the Fukushima nuclear plant, he said: "That is the obvious assumption."