WASHINGTON (AFP) - The US Central Intelligence Agency (CIA) thinks that North Korea's leader Kim Jong Un is a rational actor who is focused on staying in power and "waking up in his own bed" each day.

But if he should suddenly not show up for work, well, don't ask US spy chief Mike Pompeo about it.

"With respect to, if Kim Jong Un should vanish, given the history of the CIA, I'm just not going to talk about it," the CIA director said on Thursday (Oct 19), when asked what would happen if Kim suddenly died.

"Someone might think there was a coincidence. 'You know, there was an accident.' It's just not fruitful," he said to laughs from a Washington audience full of national security officials.

The US agency has a dark history of involvement in plots to overthrow or eliminate leaders in countries such as Iran, Cuba, Congo, Vietnam and Chile.

North Korea alleged earlier this year that the CIA working with South Korean intelligence had tried to kill Kim, 33, without offering any proof.

Pompeo, speaking to a forum held by the Foundation for Defence of Democracies, stressed that US policy was to "diplomatically and economically challenge the North Korean regime" to convince Kim to pull back on his emerging nuclear threat to the United States.

"Kim Jong Un's mission is just to stay in power," he said.

But Pompeo, who became director of the CIA in January, added that he was revitalising the agency's field missions.

"We are going to become a much more vicious agency," he said.