A LARGE explosion occurred in the northern part of North Korea last Thursday, sending a huge mushroom cloud into the air on the anniversary of the state's foundation, South Korean news agency Yonhap reported yesterday.
The South Korean government said that it was trying to confirm the report of an explosion in Yanggang province, near the border with China.
Yonhap carried reports from unidentified sources, with one in Washington speculating that the incident could be related to a natural disaster such as a forest fire.
It also cited a diplomatic source in Seoul who raised the possibility of an accident or a nuclear test.
Yonhap later quoted South Korean presidential office spokesman Kim Jong-min as saying: "Currently, we are trying to find out in detail the exact character, cause and size of the accident, but we don't think North Korea conducted a nuclear test."
Although North Korea is believed to be developing nuclear weapons, international experts would probably have been able to detect a test if one had occurred.
"We understand that a mushroom-shaped cloud about 3.5 to four kilometres (2.2 miles to 2.5 miles) in diameter was monitored during the explosion," the source in Seoul told Yonhap.
The agency also quoted an unidentified government official as saying that there had been seismic activity related to two blasts in North Korea at 11pm on Wednesday and 1am on Thursday.
Experts have speculated that North Korea might use a major anniversary such as that of the state's founding to conduct a nuclear-related test, but South Korean analyst Koh Yu Hwan said that an open test, as opposed to one below ground, would be difficult in such a small country.
"It's difficult to say, but it won't be easy for North Korea to conduct a nuclear test without resulting in massive losses of its own people," said Mr Koh.
"I think there is a possibility that it is a simple accident, rather than a deliberate nuclear test."
Yonhap's diplomatic source in Seoul said that the explosion had taken place "not far" from a military base that holds ballistic missiles.
The damage and crater left by the explosion in Kim Hyong Jik county was big enough to be noticed by a satellite, a source in Beijing told Yonhap.
On Saturday, a North Korean spokesman said that recent revelations that South Korea had conducted secret nuclear experiments involving uranium and plutonium had made his country more determined to pursue its own nuclear programmes.
South Korea insists that the experiments were purely for research and did not reflect a desire to develop weapons.
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