North Korea's claim to have tested a nuclear weapon on Monday may never be confirmed because the blast was so weak, although if the device was indeed nuclear, the test was a flop, a French nuclear official said on Wednesday.
"There is a series of differentiations to be done" to sift out the blast from background noise among the seismic data recorded on Monday, said Xavier Clement, spokesman of France's Atomic Energy Commission.
"It is possible that this cannot be done, given the weakness of the signals compared to the background noise" of subterranean movement, he said.
"If it turns out to have been a nuclear test, it's clear that the weakness of the energy released corresponds to an explosion that fell short of what could have been expected," he said.
Clement agreed with other estimates that measured the explosion at less than one kilotonne of TNT.
The seismic waves detected "are virtually at the lowest threshold of detection" by the networks of sensors deployed to monitor nuclear tests, he said.
Asked whether it would be possible to distinguish between a nuclear blast and conventional explosives, he said, "The probability that we can't is not at all negligible."
Earlier yesterday, French Defense Minister Michele Alliot-Marie said that "whatever the case, if indeed it was a nuclear explosion, then it was a failed test."
"Given its weakness, it is hard to say if it was an explosion with a large amount of conventional explosives or indeed nuclear," he said.