President Yoon Suk-yeol said Tuesday that North Korea has nothing to gain from nuclear weapons, a day after the North said it carried out exercises on mobilizing "tactical nukes" and rejected any chances of negotiations.

North Korea has ratcheted up tensions with a series of provocative missile launches in recent weeks, including one that flew over Japan in a demonstration of its ability to strike targets in the US territory of Guam.

On Monday, the North also said that leader Kim Jong-un gave guidance during the recent series of tests, including exercises on loading missiles with tactical nuclear weapons and firing a nuclear-capable ballistic missile from under a reservoir.

"North Korea is steadily developing and advancing its nuclear weapons and threatening not only the Republic of Korea but the world, but I believe it has nothing to gain from nuclear weapons," Yoon told reporters as he arrived for work.

Yoon said that as the nuclear threat is "growing serious by the day," South Korea will ready itself and respond based on a firm alliance with the United States and trilateral security cooperation with the US and Japan.

He reassured the people not to worry and to focus on their economic activities and livelihoods.

When asked if he thinks his administration's policy on North Korea remains effective in pushing the North toward the ultimate goal of complete denuclearization, Yoon said he does.

"North Korea's denuclearization has been sought over the last 30 years since the early 90s under the aim of the complete denuclearization of the Korean Peninsula, which saw us having our tactical nukes withdrawn," he said.

The US introduced tactical nuclear weapons to South Korea in the late 1950s but withdrew them in the early 1990s following a disarmament deal with the then Soviet Union and amid the then South Korean government's efforts to promote reconciliation with the North.

Asked to address calls for the redeployment of tactical nukes to South Korea, Yoon declined to comment publicly but said he is listening carefully to opinions in both South Korea and the US

Yoon also dismissed concerns raised especially among opposition politicians that strengthening military cooperation with Japan, as seen in recent trilateral naval exercises with the US, could set the stage for the stationing of Japanese troops on the Korean Peninsula.

"What concern can be justified before the threat of nuclear weapons? That's what I think," he said.

South Koreans have reacted sensitively to the issue of military cooperation with Japan due to haunting memories of Tokyo's 1910-45 colonial rule of the Korean Peninsula. (Yonhap)