The U.S. is monitoring reports that North Korean leader Kim Jong Un is in grave condition after undergoing surgery, a U.S. official told CNN on Monday.

South Korea’s Yonhap news agency, however, cited a government official there who said the reclusive leader was not seriously ill.

The conflicting reports come after Reuters cited a news outlet run mostly by North Korean defectors based in South Korea on Monday evening claiming Kim was recovering after a cardiovascular procedure.

“My understanding is that he had been struggling [with cardiovascular problems] since last August but it worsened after repeated visits to Mount Paektu,” one unidentified source told the South Korean news outlet.