Diplomats do not talk publicly about what comes after Kim Jong-il, the convalescing dictator who has turned North Korea into a rogue nuclear state.

Hillary Clinton, on her first trip as Secretary of State, brought up the topic with reporters on her plane.

"If there is a succession, even if it's a peaceful succession, that creates more uncertainty and it may also encourage behaviours that are even more provocative, as a way to consolidate power within the society," she said.

The question is whether Mrs Clinton made a beginner's error that could upset other countries in the negotiations, such as China, or whether she showed refreshing candour - the kind of approach that could shake loose what has been a diplomatic deadlock for eight years.

The answer was not clear in the hours after Mrs Clinton landed in Seoul to hold meetings with Korean leaders; neither China nor North Korea issued any official reaction to her comments.

But some experts are fretting. "If you're looking for ways to change the dynamic, there are other ways to do it," said Steve Clemons, the director of the American strategy program at the New America Foundation, a public policy research group.

"Asia is all about face. What she's done is to create a huge face problem for the North Korean Government," he said.

Senior State Department officials said Mrs Clinton was merely stating the obvious. Mr Kim, who suffered a stroke in August, has not returned to his old form and his country is behaving in a way that bears the hallmarks of a nation in the throes of a power struggle.

Mr Kim, 67, recently dismissed his defence minister, one of his closest advisers. There are conflicting reports over whether Mr Kim anointed his youngest son as his successor.

The jockeying for power in North Korea raised the pressure on the US, South Korea, China, and other countries to revive negotiations, Mrs Clinton said.

She did not speculate about how succession might play out. She said she first wanted to consult officials in South Korea and China.

The comments from the top American diplomat are certain to provoke a sharp reaction from Pyongyang. Hours earlier, the North Korean regime had stepped up its confrontational rhetoric, saying its forces were "fully ready" for war with South Korea.

Yesterday, after talks with the South Korean Foreign Minister, Yu Myung-Hwan, Mrs Clinton warned North Korea to stop provocative actions. She said it would not improve relations with the US by insulting the South and refusing talks.

North Korea's bellicose behaviour has cast a shadow over Mrs Clinton's visit to Seoul and will also figure strongly when she flies to Beijing for a meeting with the President, Hu Jintao, this weekend.

At a news conference yesterday with Mrs Yu, Mrs Clinton expressed no qualms about raising the succession issue. She said North Korea did not have a vice-president or a prime minister.

But she said "it is clear we are dealing with the Government that exists right now".

The Washington Post and Agencies