(ATTN: COMBINES related stories, CHANGES headline and lead, ADDS analyst comments)
By Choi Kyong-ae and Kim Soo-yeon
SEOUL, Sept. 9 (Yonhap) -- North Korea conducted its fifth nuke test Friday in a clear show of defiance against the international community's calls for it to halt its nuclear and missile programs.
North Korea confirmed the test four hours after seismic waves from a magnitude-5 artificial earthquake were detected around 9:30 a.m. near the North’s Punggye-ri nuclear test site.
The North claimed through its state media that the test was not only a success but the country has been able to standardize its nuclear warhead so it can be put atop a ballistic missile.
"We estimate the North has carried out its biggest test to date with the device giving an explosive yield reaching 10 kilotons," South Korea's Joint Chiefs of Staff (JCS) said in a statement. The yield was higher than an estimated six kilotons detected in January's nuclear test.
The United States and its allies, including Seoul and Tokyo, expressed grave concern as the North boasted of its improved capability to build a "smaller but stronger" nuclear warhead. Even China, Pyongyang's closest ally, said it will participate in discussions for additional international sanctions against the communist state.
Immediately after the artificial quake, South Korea's military held an emergency video conference headed by JCS Chairman Lee Sun-jin and placed its military forces on full alert so Seoul could react "sternly and strongly" in case of further provocations.
"If there is any sign of the use of nuclear weapons from North Korea, we will make a preemptive strike against the North's leadership in close cooperation with the U.S.," Leem Ho-young, chief director of the strategic planning directorate at JCS, told reporters at a briefing.
It is the first time that the Seoul government has mentioned a preemptive strike against North Korea in case of signs of a nuclear attack by its northern neighbor.
Seoul is ahead of Pyongyang in overall missile technology. It will further bolster missile capabilities in power and precision to counter ever-growing threats from the North, Leem said.
Citing the nuclear test as a "grave provocation," the Seoul government pushed the Kim Jong-un regime to give up its nuclear and missile programs completely and irreversibly in a transparent manner.
"This (nuclear test) is a clear violation of U.N. Security Council resolutions and a grave challenge to the international community," President Park Geun-hye said during an emergency meeting with her aides in Laos, the last leg of her three-nation trip that also included China and Russia.
She cut short her trip and returned home to handle the urgent security issues.
The National Intelligence Service (NIS) warned Pyongyang may conduct sixth and seventh nuclear tests at any time it wants. “The latest detonation is more powerful than the previous four tests but does not seem to be a hydrogen bomb," it said. Pyongyang had claimed it detonated a hydrogen bomb earlier this year.
North Korea has escalated its saber-rattling since it conducted the fourth nuclear test in January and test-fired a series of ballistic missiles following that. It has stepped up its efforts to improve its nuclear and missile capabilities simultaneously in order to have a nuclear-armed missile that could strike the U.S. mainland.
To achieve the goal, North Korean experts expected Pyongyang will continue its nuclear weapons tests.
"Strong international sanctions imposed in March following the January test didn't discourage the North's nuclear weapons and missile ambitions. If not support from China, the North won't budge at all," according to Kim Dong-yub, a North Korean expert at Seoul's Kyungnam University.
"There seem to be definite advancement in the technology needed to produce a miniaturized nuclear warhead as North Korea mentioned the warhead's standardization for the first time," Kim said.
Pyongyang, meanwhile, conducted its fifth nuclear test on the 68th anniversary of the founding of North Korea's government and just days after world leaders, including U.S. President Barack Obama and President Park Geun-hye, gathered in China for the G-20 summit of advanced and emerging economies.
Related to the latest test, nuclear weapons experts said the bomb that the United States dropped on Hiroshima had a 16 kiloton yield. The North's yield had about 60 percent of the destructive power of the U.S. bomb, which turned the Japanese city into ashes during World War II.
The epicenter is believed to be the same location where the North conducted its fourth test in January. Pyongyang also conducted nuke tests in 2006, 2009 and 2013.
In March, the U.N. Security Council slapped its toughest sanctions on Pyongyang for its nuclear test and long-range rocket launch early this year.
North Korea had been threatening to conduct a fifth nuclear test, claiming it has the full capacity to carry out pre-emptive nuclear strikes. In March, North Korean leader Kim Jong-un ordered his officials to conduct a nuclear warhead test and more test-fires of ballistic missiles as soon as possible.
North Korea has thus far launched a total of 22 ballistic missiles this year alone. This is more than all of the ballistic missiles launched during the 18-year reign of Kim’s late father, Kim Jong-il.
In regards to North Korea's latest act, the White House said it is aware of the seismic activity near the North's nuclear site.
"We are aware of seismic activity on the Korean Peninsula in the vicinity of a known North Korean nuclear test site," National Security Council spokesman Ned Price said. "We are monitoring and continuing to assess the situation in close coordination with our regional partners."
Other countries like Japan were quick to respond, with Prime Minister Shinzo Abe saying North Korea's additional nuclear test can never be tolerated and that if it turns out to be true, Japan cannot help but express strong protest.
Seoul, Tokyo and Washington agreed to push for "additional" and "strong" measures against Pyongyang's latest nuclear test, suggesting that there will be more punitive action against the communist country's continued pursuit of nuclear weapons.
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