"The North Korean regime will probably be removed from the map if it uses developed nuclear weapons against South Korea or the United States," Defense Minister Song Young-moo said at a security forum in Singapore, which was webcast live.
He dismissed the Kim Jong-un regime's talk of a nuclear strike as a "propaganda" strategy, not something that will actually happen.
"It's an anachronistic idea that North Korea will use nuclear weapons for the unification (of the two Koreas)," he said, responding to a question after a keynote speech at the Fullerton Forum hosted by the International Institute for Strategic Studies.
Song also defended the Moon Jae-in administration's efforts for dialogue with the North.
"It may be a rough path that could take a long time. But I think we have to go that way by being patient and patient again," he added.
He stressed that Seoul will never acknowledge Pyongyang as a nuclear power under a firm policy that deals resolutely with its provocation.
South Korea will continue efforts to achieve the "complete, verifiable and irreversible denuclearization" of the Korean Peninsula by use of every possible means, including sanctions and dialogue, he said.
"(It's a) process toward peace and our goal and our basic position that can never be yielded," he added. "In particular, I would like to say clearly that the policy of sanctions and pressure for a resolution to the North Korean nuclear issue is meant to draw North Korea into dialogue, not an aim in itself."
Song, a former Navy admiral and chief of naval operations, suggested that the navies of South Korea, the U.S., Japan, China and Russia hold a joint forum on peace and maritime order in Northeast Asia.
If launched, it would have potential to develop as a forum to involve Southeast and West Asian nations, he said.
It's the first time that a South Korean defense chief has delivered a keynote address at the Fullerton Forum, a prelude to the annual Asia Security Summit, widely known as the Shanggri-La Dialogue, held in the city state.
Singapore is the first leg of Song's three-nation tour of Southeast Asia.
He had meetings with his Singaporean counterpart Ng Eng Hen and Prime Minister Lee Hsien Loong later Monday.
The minister also plans to visit Indonesia and Thailand.
On the weekend, Song had bilateral talks with the U.S. Secretary of Defense Jim Mattis in Hawaii, where the two defense chiefs reaffirmed the ironclad alliance between the two countries in the face of the North's recent peace offensive.
They emphasized that "any efforts to drive a wedge in the U.S.-ROK (South Korea) alliance would fail," according to a press release. Source from the Yonhap.
