SEOUL — Now that the Beijing Olympics are history, North Korea’s strongman leader, Kim Jong-un, is primed to order tests of more missiles or even of another nuclear warhead.  

A Washington think tank at the Stimson Center that tracks North Korea, 38 North, has what looks like evidence that the nuclear reactor in the North’s nuclear complex at Yongbyon, north of Pyongyang, is humming away — producing more warheads.

“Snow melt on the turbine building,” says 38 North, “may be related to equipment installation and testing” near the Experimental Light Water Reactor.

The report does not suggest specifically that Mr. Kim is about to order another nuclear test, but analysts believe that North Korean scientists, engineers, and technicians are busy fabricating warheads. Mr. Kim ordered his country’s most recent nuclear test in September 2017, while President Trump was inveighing against North Korea at the United Nations, calling Mr. Kim “rocket man.” It was the sixth such test.

Then too, the report goes on, “warm water discharge — a key indicator of reactor operations — has been observed since late last year and continues to date, as evidenced by the darkened area at the discharge point and the ice-free portion of the river.”

Perhaps more immediately — and a prospect that is almost as alarming, in the view of diplomatic observers — Mr. Kim may be planning to test an intercontinental ballistic missile capable of carrying a warhead to targets in America. North Korea conducted its last ICBM test in November 2017.

The North tested a hypersonic missile on January 30, just before the opening of the Beijing Olympics. The missile, with a speed a dozen times that of sound, was a Hwasong-12 capable of reaching targets just about anywhere in Japan or Guam, where the U.S. has major air and naval bases.

“Unlike its longer range counterparts designed primarily to be able to deliver nuclear warheads to the United States mainland, the Hwasong-12’s main role is to target American military facilities on Guam — namely Andersen Air Force Base and Guam Naval Base,” said Daily NK, a website in Seoul that often reports from contacts inside North Korea.

Those bases “are central to the U.S. Military’s ability to project power in the Western Pacific,” said Daily NK. “Secondary roles include holding other key hubs of the U.S. Military’s regional supply lines such as the growing facilities on Tinian Island and Wake Island under threat, both of which are within the missile’s range.”

Since testing the Hwasong-12, North Korea has held back on more tests, presumably at the request of the Chinese, for the duration of the Beijing Olympics. Although North Korea did not participate in the Olympics, the North relies upon China for all its oil, half its food, and other vital products needed for survival. North Korea has just reopened its borders with China to highly limited trade and traffic after having closed them at the outset of the pandemic in early 2020.

Meanwhile, South Korea’s president, Moon Jae-in, has been pressing for America, China, and North and South Korea to agree to an “end-of-war” declaration certifying that all sides agree that the Korean War is definitely over at last. The war ended in July 1953 in a truce that never morphed into a formal peace treaty.

On Monday, the South’s unification ministry again called for a return to dialogue despite fears that another missile test would destroy any chance of dialogue before the South’s presidential election on March 9. A spokesman for the ministry said the government was ready for “all possibilities,” good or bad, according to Yonhap, the South Korean news agency.