North Korean leader Kim Jong-Un, who has not been seen in public for more than a month, is believed to be staying outside Pyongyang, South Korea's defence chief said Tuesday.

"As far as I know, (Kim) is staying at a certain place north of Pyongyang," Defence Minister Han Min-Koo said when lawmakers visited his office for a regular parliamentary inspection of military affairs, without elaborating on Kim's whereabouts.

"I have received reliable information from our defense intelligence headquarters," Han was quoted as saying by the Yonhap news agency. There was no official comment from the defence ministry.

Kim's absence from the public eye has triggered speculation of a debilitating illness and even rumours of a coup in Pyongyang.

His unexplained absence loomed large over a surprise visit on Saturday by a trio of his top officials and close aides to South Korea.

South Korean Unification Minister Ryoo Kihl-Jae, who held talks with the delegation, said on Sunday that one member, Kim Yang-Gon, had insisted the young leader had no medical issues.

"There is nothing wrong with the health of Secretary Kim," Ryoo quoted Kim Yang-Gon as saying.

Kim Yang-Gon heads a ruling party department in charge of South Korea-related affairs, and his reported comment was the first by a senior official on Kim Jong-Un's well-being.

No explanation was provided for why Kim has dropped from public view since he was last seen attending a music concert with his wife on September 3.

Before Kim dropped out of sight, footage shown on state TV had shown him walking with a pronounced limp.

Kim, believed to be 30 or 31, is a heavy smoker and has noticeably gained weight since taking over as paramount leader following the death of his father Kim Jong-Il in 2011.

Prior to Kim Yang-Gon's comment, the only word from the North had been a media report that Kim was in some "discomfort".

Kim's failure to attend a rare second session of the North's rubber stamp parliament last month ramped up speculation that he was seriously ill or injured.

It is by no means unprecedented for a North Korean leader to drop out of the public eye for a while, but it is more noticeable with Kim, who has maintained a particularly pervasive media presence.

A key indicator will come on Friday when the North celebrates the anniversary of the founding of the ruling Workers' Party.