The Seoul government has resumed anti-Pyongyang propaganda broadcasts along the heavily fortified border with North Korea. As the rogue state has crossed the red line again by testing what it claimed to be a hydrogen bomb, the South’s strong reaction is warranted.

The South’s loudspeakers installed along the Demilitarized Zone began to blurt out messages critical of the North’s young leader at noon on Friday, two days after it carried out its fourth nuclear weapons test.

The propaganda broadcasts may seem to be an old-fashioned, ineffectual way to punish the North for its reckless behavior. Yet they have proved to be one of the few options the South has that can inflict real pain on the unruly regime.

The broadcasts target the North’s Achilles’ heel – the young leader’s lack of legitimacy and ruthless leadership style. They can also shake the self-isolated regime to the core by sharing outside information. It is for this reason that Kim Jong-un is said to detest the broadcasts most. 

But he has asked for their resumption by conducting a nuclear bomb test, which the Seoul government rightly saw as a grave violation of the Aug. 25 inter-Korean agreement.

The agreement was hailed as a breakthrough in inter-Korean relations as it turned a crisis caused by the North’s land mine attack into an opportunity for the two sides to move toward reconciliation.

The land mine attack maimed two South Korean soldiers, prompting the South to resume propaganda broadcasts for the first time in 11 years. It hit a raw nerve with the North, which reacted strongly, warning the South to end the broadcasts and dismantle all loudspeakers or face “strong military action.”

The two sides then reached a deal, in which the South agreed to stop the broadcasts “unless an abnormal situation occurs,” while the North agreed to hold reunions of families separated by the Korean War.

Pyongyang has thrown the agreement into the trash by pushing ahead with the fourth test, forcing the South to reactivate the loudspeakers.

While resuming the propaganda broadcasts, Seoul also needs to press China to step up pressure on the North. China said it did not receive any prior notice from Pyongyang about Wednesday’s nuclear test, suggesting its influence on its belligerent ally was limited.

Yet China still holds the key to implementing any international sanctions against the North as it is the impoverished country’s economic lifeline. Beijing is opposed to the North becoming a nuclear weapons state, but it has been reluctant to take punitive actions against its nuclear provocations. All previous U.N. sanctions lacked teeth because of China’s failure to implement them in earnest.

Following the North’s latest provocation, Beijing said it would play a constructive role in imposing new U.N. sanctions, but its track record leads us to suspect its sincerity.

Now Beijing should realize that its current approach to the North Korean nuclear problem has failed. The pariah state has made it clear that it is not interested in any multilateral talks aimed at dismantling its nuclear programs. Beijing turns a blind eye to this, sticking to the view that the knotty problem can be resolved by reactivating the stalled six-party talks. If Beijing is really determined to stop the North’s nuclear program, it should show it in deeds rather than in words.