(Bloomberg) — The U.S. is seeking details about Kim Jong Un’s health after receiving information that the North Korean leader was in critical condition after undergoing cardiovascular surgery last week, U.S. officials said.The Trump administration wasn’t sure of Kim’s current condition, said the officials, who asked not to be identified. One of the officials said the White House was told that Kim took a turn for the worse after the surgery, while CNN earlier cited a U.S. official with direct knowledge saying the North Korean leader may be in “grave danger.” The White House declined to comment.The news rocked South Korean stocks, with the benchmark Kospi gauge extending losses to as much as 3% even as local defense stocks rose. Kang Min-seok, a spokesman at South Korea’s presidential office, said there was nothing to confirm on speculation over Kim’s health and nothing unusual had been detected in North Korea so far. South Korea’s Ministry of Foreign Affairs said Seoul and the U.S. are communicating closely as always.The health of Kim, 36 and a heavy smoker, is one of North Korea’s most closely guarded secrets, typically only known by a handful of people in the inner circle of leadership. While North Korea had scaled down major events as it battles the coronavirus pandemic, speculation about Kim had been growing since his unprecedented absence from April 15 celebrations for the birthday of his grandfather and state founder Kim Il Sung, one of the biggest days on the country’s calendar.Even the most well-informed North Korea experts find it hard to tell what’s happening in the secretive state. The Daily NK, a Seoul-based website that gathers information from informants inside the isolated nation, separately reported that Kim underwent a “cardiovascular surgical procedure” and was now mostly recovered. Reuters cited an official with the Chinese Communist Party’s International Liaison Department saying that Kim was not believed to be critically ill.Any leadership crisis in North Korea could potentially have serious ramifications for regional stability, as well as for talks with the U.S. over the country’s nuclear arsenal. Kim, who took power in 2011 following his father’s 17-year reign, developed the capability to deliver a nuclear warhead to any part of the U.S. before engaging in direct talks with President Donald Trump over his arsenal and sanctions imposed on the state.“When Kim Jong Un came to power, his path to leadership had been carefully cultivated by his father’s guidance and maneuvering,” said Mintaro Oba, a former U.S. diplomat who was responsible for Korean Peninsula issues. “Now there is no clear transition plan and no clear future leader. There would be a great amount of uncertainty in North Korea, and potentially, major power struggles and internal instability.”White HorseKim has been shown in state media in recent months appearing at military drills and riding a white horse on the country’s revered Mt. Paektu, where state propaganda says his grandfather used as a guerrilla base to fight Japanese colonial occupiers. North Korea’s state media reported on April 11 that Kim attended a Politburo meeting of the ruling Workers’ Party of Korea. The next day it said he inspected a military unit, but didn’t reveal the date of that visit.South Korea’s Unification Ministry said Friday it was “inappropriate” to speculate about the reasons for Kim’s absence. Kim has made 17 public appearances this year that were mentioned in state media — at a pace of a little more than one a week — the ministry said. That’s slightly down from 84 public appearances last year.South Korean intelligence said Kim Jong Un married Ri Sol Ju, a former singer, in 2009. They are thought to have three children, but there is no official mention of their offspring. Dennis Rodman, the offbeat basketball great who visited Kim in North Korea, said in 2013 he held the leader’s baby girl in his arms, a daughter named Ju Ae.While there’s been little time for him to groom a successor, Kim raised the status of his younger sister Kim Yo Jong as a key player in the secretive state. She was thrust into the global spotlight when she served as envoy to the 2018 Winter Olympics in Pyeongchang, South Korea, and became the first member of the immediate ruling family to visit Seoul.(Updates with South Korea foreign ministry spokesperson in third paragaph.)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2020 Bloomberg L.P.