North Korea fired four ballistic missiles Monday, and a day later, its state-run news agency said the country had conducted a missile launch exercise targeting US military bases in Japan.

The report did not disclose when the drill was carried out, but it was apparently referring to Monday’s missile launch.

The missiles were fired from a site on the west coast, not far from the border with China, flew about 1,000 kilometers and landed in the exclusive economic zone of Japan.

It came 22 days after it launched Pukkuksong-2, an intermediate range ballistic missile.

The latest provocation is part of the North’s program to develop nuclear missiles, and reflects Pyongyang’s strategy to deal with the security issue of the Korean Peninsula militarily not through dialogue.

The North fired missiles even when the international community was tightening economic sanctions against it and Washington was considering preemptive strikes and redeploying tactical nuclear weapons. The missile launch has shown it will put up with pressure as it develops nuclear missiles. Using negotiations to get its leader Kim Jong-un give up his nuclear ambitions looks out of the question.

Worrisome about Monday’s missile launch is that they were fired without any earlier signs that they would happen. North Korea may have converted its mid-range missiles into ones using solid rocket fuel like the Pukkuksong-2. Solid fuel requires less fueling time, making it harder to detect an imminent launch.

South Korea needs to establish a multilayered defense shield. North Korea is expected to be able to mount nuclear warheads onto its missiles in a near future.

A single nuclear weapon would devastate Seoul. To defend the capital, South Korea should have a tightly knitted network of precise missile interceptors, including the THAAD battery to be based in Seongju, North Gyeongsang Province.

The US began the process of deploying the system here Tuesday.

The navy should equip its Aegis ships with missiles to intercept coming missiles.

The US is reportedly weighing every possible option to deal with North Korean nuclear threats, with its policy expected to be outlined late this month or next month. Monday’s missile launch will likely tilt Washington toward cementing a tougher stance.

Acting President Hwang Kyo-ahn held phone talks with US President Donald Trump on Tuesday to discuss countermeasures to the North Korean provocation.

Their talks served as a warning to Pyongyang that the two allies are responding to its threats rapidly.

With Pyongyang escalating its threats to the national security of the South, the government needs to re-examine its North Korea policy completely. Its existing measures have been ineffective in curbing Kim Jong-un’s ambition to deploy nuclear missiles.

Now is the time to consider tactical nuclear weapons positively and to discuss nuclearizing the military. The North is nearing the completion of its nuclear missile program.

Its missile launch makes China’s opposition to THAAD deployment less justifiable. Yet it is stubborn in opposing the antimissile system.

South Korea, Japan, and the US all condemned North Korea for firing missiles Monday, urging further sanctions, while China called for related countries to refrain from escalating tension and said its opposition to the THAAD remained unchanged.

Kim Jong-un must be counting on Beijing. Apparently believing it will back him up eventually, he has used his nuclear and missile programs as a saber to rattle.

Even as North Korea was criticized over the poisoning of Kim Jong-nam, Kim Jong-un’s half brother, in Malaysia, Beijing invited North Korea’s Vice Foreign Minister Ri Kil-song to reaffirm their friendship. Ri returned home on Saturday, and two days later Pyongyang fired the four missiles.

Kim Jong-un has defied the international community. China should know North Korea’s nuclear missiles would destabilize Northeast Asia and ultimately hurt its national interests. Before he crosses a red line, Beijing should work harder to press Pyongyang to scrap its nuclear weapons and missile program.