PYONGYANG, North Korea - Two groups of prominent South Koreans with ties to Pyongyang travelled Monday to North Korea to pay respects to late leader Kim Jong Il, as state media indicated his son is preparing to take over power and uphold his father's "military-first" policy.

The South Korean delegations with a total of 18 people crossed the heavily fortified border for a two-day trip during which they would visit Pyongyang's Kumsusan Memorial Palace where Kim's body is lying in state, according to Seoul's Unification Ministry.

The two groups are led by the widow of former President Kim Dae-jung, who held a landmark summit with Kim in 2000, and Hyundai Group Chairwoman Hyun Jeong-eun, whose late husband had ties to the North. The North sent condolences delegations to South Korea when the two's husbands died.

South Korea has only allowed the two groups to visit and pay condolences for the death of Kim on Dec. 17. That has angered North Korea, which subsequently warned such an obstruction would lead to "catastrophic consequences" for relations between the rivals.

"I hope our North Korea trip will help improve South-North Korean ties," Lee said in a message read by an aide ahead of her departure.

While millions of North Koreans continue to mourn Kim, North Korea is offering hints about his youngest and third son Kim Jong Un's rise and the future composition of his inner circle. North Korea began hailing Kim Jong Un as "supreme leader" of the 1.2-million strong military over the weekend as it ramps up its campaign to install him as ruler.

Kim Jong Un, who is in his late 20s and was unveiled in September 2010 as his father's choice as successor, will be the third-generation Kim to rule the nation of 24 million.

Koreans should become "eternal revolutionary comrades" with Kim Jong Un, "the sun of the 21st century," the North's main Rodong Sinmun newspaper said Sunday in a commentary carried by the official Korean Central News Agency.

State television also showed Sunday footage showing Kim Jong Un's uncle and key patron, Jang Song Thaek, wearing a military uniform with a general's insignia, a strong sign he'll play a crucial role in helping the young man hold a grip on power and inherit his father's trademark "military-first" policy. Seoul's Unification Ministry said it was the first time Jang, usually seen in business suits, had been shown wearing a military uniform on state TV.

Jang, a vice chairman of the powerful National Defence Commission, is the husband of Kim Kyong Hui, younger sister of Kim Jong Il and a key Workers' Party official. South Korean lawmakers say intelligence officials have predicted that Jang and his wife will play larger roles supporting Kim Jong Un.

North Korea is in official mourning until Kim Jong Il's funeral Wednesday and a memorial Thursday.

On Saturday, Kim Jong Un again visited the Kumsusan palace to pay respect for his father -- this time as "supreme leader of the revolutionary armed forces" and accompanied by North Korea's top military brass, according to KCNA.

The North's state TV repeatedly showed Sunday footage of wailing uniformed soldiers, many with shaved heads, and other citizens professing their tear-choked longing for Kim Jong Il as they visited mourning sites.