A top North Korean defector Thursday said he had obtained the last will and testament of Kim Jong-Il, in which the late leader purportedly urges his nation to develop weapons of mass destruction.

"Keep in mind that constantly developing and keeping nuclear (weapons), long-range missiles and biochemical weapons is the way to keep peace on the Korean peninsula, and never drop your guard," the will said, according to Japanese weekly tabloid magazine Shukan Bunshun.

The report comes as poor but nuclear-armed North Korea is planning to launch a rocket that it says will put a satellite in orbit to mark the centenary of the birth of late founding president Kim Il-Sung, the father of Kim Jong-Il.

Lee Yun-Keol, the head of respected South Korean think-tank NK Strategic Information Service Centre (NKSIS), obtained the will from "a person very close to a top North Korean official", the Japanese magazine said.

Lee is a 44-year-old defector who was educated in North Korea's elite science school before fleeing in 2001 and arriving in South Korea in 2005.

According to the NKSIS, he worked as a scientist in the state organisation charged with promoting the health and longevity of Kim Il-Sung and Kim Jong-Il, who died last December.

Lee, who says he remains in touch with his former colleagues in the North, told AFP that the contents of the magazine's report were accurate.

The best-selling Shukan Bunshun did not print an image of the will, but reproduced a number of quotes it said were taken from the document.

"We have to win the psychological war with the United States. By standing up imposingly as a legitimate nuclear power, we have to weaken American influence in the Korean peninsula and work toward lifting international sanctions to prepare external conditions for economic development," it said.

Kim Jong-Il apparently had a cautious view of North Korea's main ally China, saying it was "the country that currently has the closest relations with us, but it could become the country we need to watch most in the future".

"Historically, China is the country that forced difficulties on our country. Keep this in mind and be careful... Avoid being exploited by China," Kim Jong-Il said, according to the report.

Earlier this year the Shukan Bunshun's publisher, Bungeishunju, published a book by Tokyo Shimbun reporter Yoji Gomi called "My father Kim Jong-Il and Me", based on emails and interviews with Kim Jong Il's eldest son, Kim Jong-Nam.

Jong-Nam's younger brother Kim Jong-Un is now in charge of North Korea, and is cementing his power with an array of events this week including the planned rocket flight. Western critics see the launch as a thinly veiled missile test.

"There have been rumours in Seoul that Kim Jong-Il left his will in writing and Seoul authorities got hold of a copy of it and are now analyzing it," professor Yang Moo-Jin at the University of North Korean Studies told AFP.