In South Korea, calling something “pro-Japanese” carries a highly negative connotation, as it brings back the image of the treacherous Koreans who had cooperated with imperial Japan, which occupied the Korean Peninsula from 1910-1945.

Lee Jae-myung, chairman of the main opposition Democratic Party of Korea, stirred up a hornet’s nest Friday by branding the joint drill on the East Sea involving South Korea, the US and Japan as a “pro-Japanese act and pro-Japanese national defense.”

It is well known that South Koreans have plenty of reservations about the nation working with Japan in the military sector, especially given that Tokyo is continuing its territorial claim over the Dokdo islets and moving to create counterstrike capabilities by revising its constitution.

Nonetheless, it is regrettable that Lee made a controversial remark that could distort fast-paced security developments on the Korean Peninsula that directly pose grave threats to the life of South Korean people.

North Korea revealed Monday that its testing of 12 ballistic missiles in the past couple weeks were simulations designed to mount a nuclear attack on targets in South Korea, confirming Pyongyang’s belligerent stance that flatly rejects offers to come to the negotiation table and resolve mounting geopolitical tensions.

What’s worrisome is that the North’s state media on Monday, marking the 77th anniversary of the foundation of the ruling Workers’ Party, disclosed photos of the military drills with North Korean leader Kim Jong-un giving guidance and said ballistic missile launches were tested for loading tactical nuclear warheads.

Pyongyang’s missile launches involving tactical nuclear warheads -- the most provocative saber-rattling in recent years -- were in response to the large-scale combined naval drills powered by a nuclear-powered aircraft carrier and an Aegis destroyer, among other military assets.

On Oct. 4, North Korea fired an intermediate-range ballistic missile over Japan into the Pacific, sending a strong alarm to Japanese authorities in a way that the latest missile threats from the North are not limited to South Korea.

Considering the North’s escalating provocations, it is imperative that South Korea should closely work with the US and Japan, as agreed upon in October 2017 when the defense ministers of the three countries concurred. Notably, that agreement was made during the Moon Jae-in administration. President Moon was elected from the Democratic Party of Korea. If Lee’s logic is applied, it is Moon who made a supposedly pro-Japanese act by sealing the military cooperation agreement.

Granted, there remains a host of thorny, emotionally charged historical issues that South Korea and Japan need to work out. But this does not mean that the country should avoid cooperating with Japan to jointly deter North from posing security threats.

The threats from North Korea have reached a point that cannot be ignored or downplayed. The North revealed Monday its Sept. 25 ballistic missile drills simulating the loading of tactical nuclear warheads were done at a silo under a reservoir in its northwestern region, suggesting the regime is sophisticating its military attack capabilities.

On Tuesday, President Yoon Suk-yeol rightly brushed off concerns from opposition politicians that joint military drills with the US and Japan could eventually lead to a much-dreaded situation in which Japanese troops would be stationed on the Korean Peninsula.

Instead of bickering over Japan, Korean politicians and security policymakers should pay attention to what North Korea wants to achieve. Last month, the North’s rubber-stamp parliament approved a new law that sets the stage for its preemptive nuclear strikes. The move was in line with Kim’s ambition to turn his reclusive country into a nuclear power.

The Democratic Party and its chief Lee should face the extremely volatile security reality as it is, and refrain from striking up the anti-Japan dispute that is not only irrelevant but also irresponsible.