North Korea has been ratcheting up its threatening moves in recent weeks, a development that should alarm South Korea’s officials in charge of security, defense and inter-Korean relations.

On Thursday, the North fired multiple short-range ballistic missiles toward the East Sea, according to the Joint Chiefs of Staff. The missiles were launched from the Pyongyang area at 7:10 a.m., but other details were not disclosed.

South Korea’s military condemned the latest launch, which tested missiles capable of hitting major cities and military facilities in South Korea, including Seoul.

The missile launch came after North Korean leader Kim Jong-un on Monday said the regime was implementing a plan to boost its number of nuclear weapons “exponentially.”

North Korea’s state media reported Kim said in a speech on the North’s founding anniversary that the country must thoroughly prepare its nuclear capability and its readiness to ensure its security rights.

Kim stated that a strong military force is required to deal with the “various threats by the United States and its followers,” and regarded what he sees as a US-led nuclear-based military presence in the Korean Peninsula as a “grave threat.”

But it is the North’s nuclear weapons and ballistic missiles that are posing serious threats to South Korea and neighboring countries.

In particular, South Korean policymakers as well as citizens are worried about the increasingly dangerous trash-laden balloon campaign by North Korea. On Sunday, one of the balloons sparked a fire in a warehouse in Paju, 28 kilometers north of Seoul. Firefighters rushed to the scene and put out the blaze.

There was another fire report related to a North Korean balloon. According to the local media outlets, one balloon caught fire in an automotive component production facility in Gimpo, Gyeonggi Province, on Sept. 5.

South Korean authorities believe that a detonation device had been attached to the balloon, with flammable materials inside. Military officials are now carrying out investigations into the issue.

Although the direct link between the fires and the balloons is yet to be confirmed, some security experts said that the new type of balloon equipped with a detonation device should be regarded as an act of terrorism targeting South Koreans, a clear violation of international law, and South Korean authorities should send a strong warning to the North.

Since May, North Korea has sent trash-carrying balloons across the border on 17 occasions, despite repeated condemnations from the South. It is more than a nuisance because it can lead to potentially life-threatening incidents and serious property damage in public and residential areas.

It should be noted that the North sent over 1,250 balloons between Sept. 4 and Sept. 8, a quantity that some experts in Seoul said was likely aimed at testing the size of balloons and measuring other details such as the weight of an object a single balloon can carry, and the impact from weather conditions.

What is worrisome is the possibility that the North is turning the balloon campaign into something that goes beyond psychological warfare. It is possible that such balloons can be easily converted into carriers of chemical weapons, experts warned.

The combination of a ballistic missile launch and trash-carrying balloons could be a thinly veiled attempt by the North to heighten inter-Korean tensions in order to divert the attention of North Koreans hit by floods and typhoons during the summer.

North Korean leader Kim is now likely to make more saber-rattling moves in the form of ballistic missile launches, nuclear weapons programs and military provocations near the inter-Korean border. The South Korean government must step up security measures and strengthen military preparedness against the North’s provocations.