Asked whether the North might have conducted a test ahead of the Chinese visit, a South Korean government analyst said: "Absolutely not. And with such a test and the cloud and also the radioactive fallout, it would have been too obvious."
Thursday was the 56th anniversary of North Korea's founding. The reclusive communist state often stages extravaganzas and big events to mark important anniversaries.
Yonhap had conflicting reports about the cause, quoting one source as saying it could have been a forest fire; another that it might have been an arms depot or factory explosion.
Other possibilities include a failed missile engine test or a high-explosives test as a precursor to a nuclear blast, diplomats said. "In the northern part of the country, there are a lot of weapons factories and underground missile bases. The rocket-fuel could have exploded in the underground base, or something," said Daniel Pinkston of the Center for Nonproliferation Studies in Monterey, California.
A large explosion occurs and we don't know if it was nuclear or not. That is disturbing, I thought we have sensors that could tell if a nuke was exploded anywhere in the world.
If you are going to plan a large explosion, tell people about it. Some one could get a little trigger happy and launch a missile, just in case you are launching missiles at other countries. "Oh we are sorry we destroyed your country, we thought you were firing at us. Next time tell us you are testing nukes.", I am not saying that will go over well internationally. Could you really could you be blamed if an automatic system destroyed a country?