But the Defence Ministry said on Monday it has no such plan, without elaborating.
Acquiring nuclear submarines is a sensitive issue for South Korea because it could trigger opposition from nations such as the United States and China amid worries about a regional arms race.
After North Korea's fourth nuclear test in January, some conservative lawmakers and scholars demanded that South Korea develop its own nuclear weapons, but the government dismissed the request.
The United States, which stations about 28,500 troops in South Korea, has long said the protective "nuclear umbrella" it provides South Korea is meant to deter an attack on its ally by North Korea.
North Korea is seeking to develop nuclear-armed missiles capable of reaching the continental US. Outside experts say the country doesn't yet have such weapons.
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