North Korea leveled up its military threat by claiming Saturday it had successfully conducted an underwater test-fire of a submarine-launched ballistic missile. Kim Jong-un, the North’s young leader, watched the missile “soar into the sky from underwater,” Pyongyang’s state media reported without specifying the exact date and location of the test-fire.

Shortly after the report, the North fired three antiship cruise missiles into the sea off its coast.

Pyongyang’s latest show of force followed repeated threats to fire without warning on South Korean naval vessels it accused of violating its territorial waters in the West Sea.

Some military experts here said the recent test signaled that the North was in the early stages of SLBM development as the missile was presumed to have flown about 200 meters after it soared from the waters. But this evaluation cannot be a reason to ease the urgency of coping with a fresh threat it is posing to the security of the Korean Peninsula and beyond. As a former senior U.S. official noted, what could be the North’s first underwater test-fire of a ballistic missile from a submarine showed its missile capabilities “are advancing at a clip that is concerning, if not alarming.”

The North’s bid to develop and deploy SLBMs possibly tipped with miniaturized nuclear warheads threatens to nullify the South’s defense posture, focused on attacks by land-based missiles. Seoul will have to modify its tactics against threats from the recalcitrant and bellicose regime.

If what the North claimed proves true, it could be regarded as having reached a point where its naval strike capability is a decade ahead of the South. The South Korean Navy has just come up with a plan to build six 3,000-ton submarines equipped with vertical missile launchers between 2027 and 2030.

The prospect of Pyongyang being armed with SLBMs is also raising the need for Seoul to expand military information sharing with the U.S. and Japan. China should exert more pressure on the North to stop its missile and nuclear weapons programs if it does not want to see the strengthening of the trilateral security cooperation.

Pyongyang’s latest show of force may also be seen as being aimed at bolstering its position ahead of a possible reopening of long-stalled multilateral talks on its denuclearization in return for economic and diplomatic incentives.

Over a week before the SLBM test-fire, a South Korean envoy had traveled to Washington and Beijing to have separate discussion with his U.S. and Chinese counterparts on resuming the six-party talks also involving Japan and Russia. The U.S. has shown some willingness of being flexible about a format for “serious dialogue” on the North’s denuclearization.

Pyongyang might have wanted, in particular, to test Washington’s readiness to restart the six-party talks. The U.S. State Department said Saturday the North’s launches using ballistic missile technology were a “clear violation” of U.N. Security Council resolutions.

It has yet to be seen whether Pyongyang’s latest show of force will build up or terminate the momentum for the resumption of the nuclear talks. What seems clear now is that it is heightening the need for Seoul and Washington to be more proactive in handling the North Korean regime ― either in engaging with or putting pressure on it.