A former North Korean spy who bombed a South Korean airliner said Wednesday that the North's leader Kim Jong-Un is struggling to control his military and using war talk to shore up support.

Kim Hyun-Hee, who said she was ordered by Jong-Un's father Kim Jong-Il to bomb the airliner in 1987 killing 115 people, said she believes the son is still trying to establish himself following his father's death in December 2011.

"Kim Jong-Un is too young and too inexperienced," she told Australia's ABC television in an exclusive interview from Seoul, where she lives at an undisclosed location surrounded by bodyguards.

"He's struggling to gain complete control over the military and to win their loyalty. That's why he's doing so many visits to military bases, to firm up support."

The North has been turning up the rhetoric for weeks and on Tuesday reiterated a warning that the Korean peninsula was headed for "thermo-nuclear" war, advising foreigners to consider leaving South Korea.

Kim Hyun-Hee told ABC there was method in the North Koreans' madness in threatening thermo-nuclear war.

"North Korea is using its nuclear programme to keep its people in line and to push South Korea and the United States for concessions," said Kim, who was captured after boarding the doomed 1987 plane in Baghdad.

She got off during a stopover in the Gulf, leaving a time bomb in an overhead compartment, but was arrested with another agent when they tried to leave Bahrain using fake Japanese passports.

Both immediately swallowed cyanide capsules. The man died almost instantly but Kim survived and was brought to Seoul, where she confessed and was eventually pardoned.

Kim published a book entitled "Tears of My Soul" describing her training at a North Korean spy school, and donated the proceeds to families of victims of the bombing.

She married one of her security guards and now lives in Seoul, still fearful that North Korean assassins could strike at any time, ABC said.