(LEAD) S. Korean military: N. Korea's blast doesn't seem to be from H-bomb
(ATTN: INCORPORATES article moved under slug 'NK test-readiness'; UPDATES from 5th para)
SEOUL, Jan. 6 (Yonhap) -- South Korea's military played down North Korea's H-bomb capability Wednesday, saying its new nuclear test doesn't appear to be hydrogen-based, given the intensity of the tremor.
The secretive North announced earlier in the day it has successfully conducted a test of a hydrogen bomb.
"It is hard to regard this test as that of a hydrogen bomb," the military said, requesting anonymity,
"Only a few countries including the U.S. and Russia have conducted hydrogen bomb tests and the size of the detonations reached 20 to 50 megatons," the official said.
The latest North Korean test amounts to 6 kilotons and it's too weak for a hydrogen bomb, he said.
The latest test was conducted differently from the previous three tests, the official said, referring to the North's "organized and intentional efforts to hide the nuclear test plan in thorough secrecy."
The Ministry of National Defense denounced the fresh nuclear detonation test as a "grave threat" to the peace of the Korean Peninsula and the world, vowing efforts to punish the communist country.
"In close collaboration under the South Korea-U.S. alliance and with the international community, our military will take necessary measures to make North Korea pay for the nuclear test," ministry spokesman Kim Min-seok said in a press briefing.
In light of the nuclear test, the Defense Ministry also put the military on alert and beefed up surveillance of North Korea.
"In addition, South Korea and the U.S. boosted the operations of their surveillance assets in order to better monitor North Korea's military movements," Kim noted.
In a 10-minute telephone conference with United States Forces Korea (USFK) commander Gen. Curtis Scaparrotti earlier in the day, Joint Chiefs of Staff Chairman Lee Sun-jin ensured close collaboration with the U.S., according to ministry officials.
Defense Minister Han Min-koo will hold another phone conference with his U.S. counterpart Ashton Carter.
Earlier in the day, a military expert well versed in the North's nuclear program called into question the validity of the country's claim of a hydrogen bomb test.
"The scale of the latest nuclear test fell short of that of the third nuclear test (in 2013)," the expert said.
The local meteorological administration put the magnitude of the tremor resulting from the test at 4.8, which is less than the 4.9 magnitude registered in the previous nuclear test three years ago.
The explosive power of a hydrogen bomb is up to 1,000 times stronger than that of an atomic bomb, and North Korea cannot afford a hydrogen bomb test inside the country, the expert stressed.
Even if the tested bomb included hydrogen, it must have been a very low-end bomb, he said.
Vice Defense Minister Hwang In-moo echoed the skepticism.
"For now, it is unlikely," the vice minister told reporters after discussing the latest nuclear test with senior members of the ruling Saenuri Party.
"It needs to be determined through further data analysis how powerful the explosion was and on what scale it was conducted," he said.