North Korea said Sunday its leader Kim Jong-un has made an “important decision to defend national security and sovereignty,” furthering speculation about an imminent nuclear test.

The young ruler convened an extended meeting of the Central Military Commission to discuss measures to “revere our party’s songun (military-first) revolutionary leadership and bring off a great changeover in increasing military power,” the North’s official Korean Central News Agency said.

During the meeting, Kim reached an “important decision that serves as a guideline to further strengthen the military” and “protect national security and sovereignty,” the KCNA said, without elaborating. 

The report marks the latest in a series of threats made by Pyongyang since the U.N. Security Council on Jan. 22 approved a new resolution and tightened sanctions in punishment for its December rocket launch.

With signs growing that the communist country is counting down to a third detonation of its atomic devices, neighbors are ratcheting up diplomacy and resorting to a show of force.

South Korea, the U.S., Japan and other countries have been warning of additional, tougher bans such as targeting its financial assets or sea cargos.

Lim Sung-nam, Seoul’s special representative for Korean Peninsula peace and security affairs, left for Beijing on Sunday apparently to push for extra pressure on its rogue ally. He is expected to meet with his Chinese counterpart, Wu Dawei, and other executives before returning Tuesday.

President-elect Park Geun-hye pledged stern action against further North Korean provocations during her meeting on Friday with Rep. Ed Royce, chairman of the U.S. House Committee on Foreign Affairs, and four other congress members.

China, for its part, has reportedly called in North Korean Ambassador Ji Jae-ryong “many times” since the communist state on Jan. 24 threatened to carry out more firings of long-range rockets and a “high-level nuclear test aimed at the U.S.”

Beijing’s signing onto the U.N. decision was a step away from its usually stiff opposition to binding penalty against Pyongyang, spawning veiled friction between the two countries.

While the North accused China of “abandoning even elementary principles” by endorsing the fresh sanctions, its biggest ally and patron hinted at slashing assistance in response to another atomic explosion, through its state-run Global Times.

China’s president-in-waiting Xi Jinping also expressed his resistance to the regime’s development of nuclear programs and other weapons of mass destruction at his meeting late last month with Park’s special envoys led by Kim Moo-sung.

Yet on Jan. 27, the KCNA reported that Kim “expressed the firm resolution to take substantial and high-profile important state measures” against the latest sanctions. Rodong Sinmun, the North’s main party newspaper, said the same day that the country now has “no other option,” saying “a nuclear test is what the people demand.”

The state-run propaganda channel on Saturday warned again that South Korea will be “retaliated against with a thunderbolt” if it takes part in imposing further sanctions. It also slammed the U.S. for holding “double standards” by denying its right to the use of space whereas “blindly conniving at” Seoul’s successful recent rocket liftoff.

Seoul’s Defense Ministry and intelligence see the North as technically ready and simply awaiting a political go-ahead.

Arousing particular concern is that this time Pyongyang may conduct multiple detonations using highly enriched uranium as the fissile material, instead of plutonium adopted in its 2006 and 2009 tests.

Satellite images point to final preparations at the North’s Punggye test site, with tunnels, radioactivity detecting devices and other relevant equipment installed at its western and southern parts. A cover has also been placed at the entrance of the site to fend off satellite monitoring by other countries.

“There has been a flurry of activity near the test site,” Gen. Jung Seung-jo, chairman of the Joint Chiefs of Staff, said Thursday, adding the military is closely watching if it is part of the North’s “deceptive strategy.”

Unification Minister Yu Woo-ik said Friday the looming test may “constitute the final stage of its nuclear development” that makes way for technological progress required to miniaturize and lighten warheads.

Amid escalating tension, President Lee Myung-bak later Sunday made an unexpected visit to the underground situation room at Cheong Wa Dae.

The military has also ordered all frontline units on standby including naval forces operating near the Northern Limit Line, the conflict-prone de facto maritime border with the North.

Seoul and Washington will begin three-day naval drills on Monday in the East Sea in an apparent show of force against the pugnacious regime.

Joining the three-day practice are the USS San Francisco, a 6,927-ton Los Angeles-class nuclear-powered submarine loaded with long-range cruise missiles, and the 9,800-ton Aegis-equipped guided-missile cruiser Shilo, both of which arrived here late Thursday.

Ten South Korean vessels will also be mobilized, including a 7,600-ton King Sejong the Great Aegis destroyer, a corvette and a new Type-214 submarine.

Their exercises will include anti-submarine, anti-aircraft and anti-ship drills, military officials said.

By Shin Hyon-hee (heeshin@heraldcorp.com)