Kim Yo-jong, Kim Jong-un’s sister, likely being formally elevated in secretive N.K. regime

A high-level change within North Korea’s notoriously secretive regime has triggered new speculation that Kim Jong-un may be on the verge of formally anointing his younger sister as his No. 2 so she can officially take control of the government should he die or fall terminally ill.

South Korea’s Yonhap News Agency reported Tuesday and Wednesday that Mr. Kim, 37, who came to power a decade ago, established the “first secretary” post during a rare ruling party congress in January in the North Korean capital of Pyongyang.

Yonhap, which is known for intensive coverage of developments relating to the Kim regime, reported that the position likely has not been filled but could go to Mr. Kim’s 33-year-old sister, Kim Yo-jong.

The development is subtle but could have wide-reaching implications.

It is unclear how the new position may impact the nuclear-armed regime’s posture toward the rest of the world.

U.S. officials closely monitor serious reports of shifts within the North Korean regime that may create openings for diplomacy or trigger provocations and escalations.

The Biden administration has kept North Korea policy on the back burner after a more than two-year stall in diplomacy involving the U.S., North Korea and South Korea. Diplomacy stalled after the Trump administration attempted to use summits between President Trump and Mr. Kim to persuade the North Korean regime to abandon an arsenal of nuclear weapons that it has built up clandestinely over decades in violation of U.N. Security Council resolutions.

Many believe Mr. Kim is prepared to wait out the Biden administration and is betting that the U.S. and its allies eventually will be forced to accept his nation as a nuclear power.

Speaking Tuesday at The Washington Brief, a monthly forum hosted by The Washington Times Foundation, analysts said President Biden’s recent White House meeting with South Korean President Moon Jae-in showed solidarity between the two countries in their approach to Pyongyang, but the levers available to pressure North Korea may be diminishing.

Optimism of the Trump era, sparked by a trio of historic face-to-face meetings between Mr. Kim and Mr. Trump, is being replaced by entrenchment in North Korea. The leadership in Pyongyang is growing more convinced that nuclear weapons are necessary to survive and is finding no pressing need to abandon the arsenal.

“Why would they give this all up?” said Joseph DeTrani, a former CIA official and longtime U.S. diplomatic adviser. “They’ve worked so long to get this. It’s a deterrent, and it provides survivability, insurance, for the regime to survive.”

A potential structural shift within the Kim regime is being reported roughly a year after rumors that Mr. Kim had undergone emergency heart surgery and fallen gravely ill triggered international headlines.

The rumors have not been confirmed. At the time, reports said Kim Yo-jong could be tapped as the familial successor to head the regime, which the Kim dynasty has ruled since her and her brother’s grandfather Kim Il-sung emerged as North Korea’s founding leader in the 1940s.

North Korea watchers have formed a consensus that Kim Yo-jong is a trusted aide of Kim Jong-un because she was at his side during the high-level summitry of the Trump era. Photographs show her running behind her brother or holding an ashtray at the ready should he need to crush a cigarette.

The brother and sister are believed to have held a close bond since studying together as children at an exclusive school in Switzerland.

A Yonhap report Wednesday cited former South Korean Unification Minister Lee Jong-seok as telling reporters that “in case of an emergency, including those involving leader Kim’s health, Kim Yo-jong is likely to take up this deputy position and act temporarily as the successor until power is handed over to Kim Jong-un’s son.”

Yonhap also cited Mr. Lee as saying Jo Yong-won, a close aide to Mr. Kim who initially was speculated to have been elected to the newly created post, is unlikely to take up the position because he is not part of the Kim family or the “Paekdu bloodline.”

• Ben Wolfgang contributed to this report.