North Korea's ruling party Saturday hailed the son of late leader Kim Jong-Il as "supreme commander" of the military, in the latest sign that the untested successor is tightening his grip on power.

Experts said the move indicated that Pyongyang would maintain its Songun (military-first) policy, blamed for the deaths of thousands of people to starvation as the isolated regime diverts resources to its armed forces.

"We will uphold Comrade Kim Jong-Un as our supreme commander and general and we will bring the Songun revolution to a completion," the Rodong Sinmun, the mouthpiece of the ruling communist party, said in an editorial.

The newspaper urged Jong-Un, Kim's youngest son, to lead North Korea to "eternal victory".

It is the first time that the North's official media has used the title supreme commander -- a post previously held by his father -- for the new leader, already a four-star general despite only being in his late 20s.

"This shows that Jong-Un now has a firm grip on the military and the North is heralding this to the outside world," professor Kim Yong-Hyun of Dongguk University in Seoul told AFP.

"It also suggests that the North will continue with its Songun policy at least in the foreseeable future."

North Korea on Monday described the untested Jong-Un as the "great successor" after announcing the death of his father at age 69.

Experts said the latest acclamation is particularly significant because it came on the 20th anniversary of the declaration of Kim Jong-Il as supreme commander.

The dynasty's latest ruler remains a figure of mystery to the outside world, which is seeking clues to future policy in the nuclear-armed nation.

The son was appointed to senior military and party posts in September 2010, paving the way for a third-generation hereditary succession after the late Kim succeeded his own father Kim Il-Sung in the 1990s.

The country's regular armed forces total 1.19 million and the regime has a policy prioritising the military's needs over those of civilians.

The elder Kim perpetuated his power using an all-pervading personality cult inherited from his father, and the North's propaganda machine has cranked into action to burnish the image of Jong-Un.

State media reported Saturday that Kim Jong-Il's "loving care" for the North Korean people lingered even beyond his death, with residents in the capital enjoying a special treat of fresh fish.

The late leader took steps on the eve of his demise to supply the rare luxury, and Jong-Un ensured the fish was rushed to the people while in mourning, according to the Rodong Sinmun.

"Salespersons and citizens burst out sobbing at fish shops in the capital," it said, carrying pictures of housewives shedding tears of gratitude.

Kim Jong-Il presided over a 1990s famine that saw hundreds of thousands of people die, and there are still chronic food shortages in the impoverished communist state, particularly outside the privileged capital.

Activists in South Korea on Saturday sent 800 pairs of winter socks carried by balloons across the border to the North, where they can be exchanged for food. Temperatures fall well below freezing during the North's harsh winters.

South Korea also confirmed that the wife of its late president Kim Dae-Jung would visit the North next week on an unofficial visit to pay respects.

Former first lady Lee Hee-Ho, accompanied by Hyundai Group chairwoman Hyun Jung-Eun, will cross the heavily militarised border and travel overland to Pyongyang, but will not stay for Wednesday's funeral, the government said.

South Korea, in a conciliatory move at a time of high tensions, on Wednesday expressed sympathy to the North's people, but not the communist regime.

It said it would permit only Lee and Hyun's delegation to visit the North to convey their private condolences. South Koreans must receive government permission for all contacts with the North.

Kim Dae-Jung and Kim Jong-Il held the first-ever North-South summit in 2000, while the Hyundai Group pioneered cross-border business exchanges.