South Korean officials on Tuesday disputed a news report that North Korea’s leader, Kim Jong-un, was receiving treatment after undergoing heart surgery.

Daily NK, a Seoul-based website that relies on anonymous sources inside North Korea to report on the isolated country, said late Monday that Mr. Kim received a cardiovascular procedure at Hyangsan Hospital, a clinic dedicated to treating the Kim family, on April 12.

The website said Mr. Kim was recuperating at a villa near the hospital, which is on the foothill of Mount Mohyang, north of Pyongyang, the North Korean capital. Most of the doctors called in from Pyongyang to treat Mr. Kim returned to the capital a week later because Mr. Kim had recovered enough, the report said, quoting an anonymous source in North Korea.