SEOUL — North Korea's state television broadcast scenes of "indescribable sorrow" after Monday's announcement of the death of leader Kim Jong-Il, as hysterical people pounded the ground in a display of grief.

The death of the 69-year-old "Dear Leader" was revealed on state television by a female announcer clad in black, who tearfully said she was reporting the news "with the gravest emotions".

Her words were aired repeatedly on state TV along with a photograph of a smiling Kim in his trademark khaki tunic. A band played solemn music.

Kim died Saturday of a heart attack, Pyongyang's Korean Central News Agency (KCNA) and the television station announced, urging people to rally behind his youngest son and heir apparent Kim Jong-Un.

It is the second dynastic succession in the history of communist North Korea, after founding leader Kim Il-Sung died in 1994 -- sparking similar scenes of organised hysteria.

"They are not even trying to wipe away tears and are convulsing with pain and despair caused by the loss," KCNA said Monday of the country's impoverished citizens, adding the population of 24 million was in "indescribable sorrow".

The state TV showed ruling party members in one North Korean county crying out loud, banging tables and sobbing.

"I can't believe it. How can he go like this? What are we supposed to do?" said one distraught cadre, Kang Tae-Ho.

In Seoul the Daily NK, an online newspaper run by North Korean defectors, said Pyongyang had mobilised large numbers of troops to strengthen security checks, shut down outdoor markets and force people to stay home.

"There are armed soldiers on the street every four metres (yards)... military and intelligence officers are on guard everywhere," it quoted a source in the northeastern city of Musan as saying.

The source said people were afraid in case they did not show enough zealotry in their mourning, recalling punishments meted out to some after Kim Il-Sung's death 17 years ago.

State TV aired non-stop footage of Kim Jong-Il's "field guidance tours" to military bases, factories, stores and other installations and urged people to follow "the spirit of the great general".

Footage from central Pyongyang showed schoolchildren, workers and the elderly alike prostrate with grief in front of portraits of Kim Jong-Il and statues of Kim Il-Sung, whose bronze presence is pervasive in the city.

"How can I express all the sorrow... I can't speak any more," a soldier said in footage shown by China Central Television before bursting into tears, as pedestrians in Pyongyang wept and covered their faces.

Some in Pyongyang pounded the ground with their fists and others wailed at the sky, in a testament to the ferocious personality cult built up around Kim Jong-Il which is now being transferred to Kim Jong-Un.

"Under the leadership of Comrade Kim Jong-Un, we will turn our sorrow into strength and courage and overcome the present difficulties and work harder for the great victory of the Juche (self-reliance) revolution," KCNA quoted Jong Il-Guk, a 43-year-old military officer, as saying.

Kim Ok-Song, a 23-year-old worker at Pyongyang Electric Wire Factory, said in the North Korean state footage: "I will change sorrow into strength and courage, and remain faithful to respected Comrade Kim Jong-Un."

All singing, dancing and other entertainment has been banned until December 29 as North Korea observes a period of national mourning, according to the Pyongyang correspondent of China's Global Times newspaper.

"The streets of the North Korean capital were much quieter than usual, with most of the shops closed and all flags lowered to half-mast," he wrote.

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