North Korea fired hundreds of artillery shells in waters near South Korean border islands on Jan. 5. Last week, it said it no longer regarded the South as inhabited by “fellow countrymen” but as a “hostile state” it would subjugate through a nuclear war. On Friday, it said it had tested an underwater nuclear drone to help repel U.S. Navy fleets.

That new drumbeat of threats, while the United States and its allies have been preoccupied with the wars in Ukraine and the Middle East, has set foreign officials and analysts wondering whether the North’s leader, Kim Jong-un, has moved beyond posturing and is planning to assert more military force.

For decades, a central part of the North Korean playbook has been to stage carefully measured and timed military provocations — some aimed at tightening internal discipline, others at demanding attention from its neighbors and the United States, or all of that at once.

But to several close watchers of North Korea, the latest round of signals from Mr. Kim feels different. Some are taking it as a clue that the North has become disillusioned with seeking diplomatic engagement with the West, and a few are raising the possibility that the country could be planning a sudden assault on South Korea.