U.S. Is Watching North Korea for Signs of Lethal Military Action

North Korea’s leader, Kim Jong-un, could take some form of lethal military action against South Korea in the coming months after having shifted to a policy of open hostility, U.S. officials say.

The officials have assessed that Mr. Kim’s recent harder line is part of a pattern of provocations, but that his declarations have been more aggressive than previous statements and should be taken seriously.

While the officials added that they did not see an imminent risk of a full-scale war on the Korean Peninsula, Mr. Kim could carry out strikes in a way that he thinks would avoid rapid escalation.

They pointed to North Korea’s shelling of a South Korean island in 2010 as an example. The two sides exchanged artillery fire, resulting in the reported deaths of troops on both sides as well as civilians in the South, but both militaries soon stopped.

Mr. Kim’s more aggressive posture has been evident through a series of actions this month. On Wednesday, the North fired several cruise missiles from its west coast into the sea, the South Korean military said. Mr. Kim’s government announced on Jan. 14 that it had tested a new solid-fuel intermediate-range missile tipped with a hypersonic warhead. And on Jan. 5, his military fired hundreds of artillery shells into waters near South Korean islands, forcing some residents to seek shelter.

At the same time, Mr. Kim has decided to formally abandon a longtime official goal of peaceful reunification with South Korea, the North Korean state news media announced on Jan. 16. Mr. Kim had signaled the move for months and said in a speech the day before that conciliatory references to unity with the Republic of Korea, as the South is officially known, must be removed from the Constitution.