North Korea's submarine missile
North Korean leader Kim Jong Un looks through a periscope of a submarine during his inspection of the Korean People's Army Naval Unit 167.KCNA via Reuters

North Korea is suspected to be building a new missile-launching system which could be placed in a submarine, says Seoul.

South Korean military has said they have detected signs of North's latest development which could end up in Pyongyang successfully setting up the submarine-launched ballistic missile (SLBM).

"There is no intelligence yet that North Korea has an SLBM in operation. But the possibility of a North Korean submarine equipped with an SLBM has been detected recently," said an official document submitted by the Joint Chiefs of Staff (JCS), according to Seoul's Yonhap news agency.

Officials from both Washington and Seoul are looking into the matter.

The Washington Free Beacon had reported two weeks ago, citing two US intelligence officials, that North is building a missile submarine. However, the US officials did not directly comment on the specifics.

Pentagon said: "We do not comment on intelligence matters, but we do urge North Korea to become more transparent in their defence sector in order to reduce tensions in the region."

The Korean People's Navy presently does not believe to possess submarine-based launching facilities and Seoul authorities fear a test-launch could be on the cards in the near future, if North Korea wants to press ahead.