North Korea has continued high-explosive detonation tests and its possible nuclear test is forecast to be much more powerful both in scale and yield than previous ones, Seoul's intelligence authorities said Wednesday.
  

"North Korea has been carrying out high-explosive tests at a test site in Pyongyang to secure technology for weapons miniaturization and stronger explosive power," an official said, requesting anonymity.
  

"Should the North conduct a fourth round of nuclear test, its explosion would have a yield of at least 10 to 15 kilotons with a larger scale compared to the previous ones," he added.
  

The North's initial underground test in 2006 was measured at 3.9 on the Richter scale with a wield of less than 1 kiloton. In May 2009, Pyongyang carried out the second test that created a 4.5-magnitude tremor with a yield of 3 to 4 kilotons.
  

During the third and the latest test in February 2013, the figures jumped to 4.9 on scale and 6-7 kilotons, according to South Korean and the U.S. authorities.
  

"No unusual signs have been detected in and around its nuclear test site of Punggye-ri in North Hamkyong Province. But Pyongyang has been ready to carry out a fresh test round whenever it wants," the official noted.
  

The communist country has repeatedly vowed to develop its economy and nuclear arsenal in tandem under the notion that the destructive weapons programs are a deterrent against what it claims is the U.S.' hostile policy against it. Last year, it threatened to conduct a "new form" of nuclear test.
  

The provocative regime was also estimated to have increased its nuclear stockpile.
  

"North Korea has revved up efforts to secure more weapons-grade plutonium and to have the highly enriched uranium program, though the exact amounts are not known," another Seoul official said on condition of anonymity.
  

In its 2014 white paper, Seoul said the North is presumed to have secured some 40 kilograms of weapons-grade plutonium, "but the figure is literally nothing but a presumption," he said.
  

On Tuesday, Joel Wit, the chief analyst running the website 38 North at Johns Hopkins University, said Pyongyang is currently believed to have 10-16 nuclear weapons -- six to eight of them based on plutonium and four to eight based on weapons-grade uranium -- and its nuclear stockpile could expand to as many as 100 weapons by 2020. (Yonhap)