The US is monitoring intelligence that North Korea's leader, Kim Jong Un, is in grave danger after a surgery, according to a US official with direct knowledge.

Kim recently missed the celebration of his grandfather's birthday on April 15, which raised speculation about his well-being. He had been seen four days before that at a government meeting.

CNN has reached out to the CIA, National Security Counsel and the State Department for comment. CNN has also sought comment from the South Koreans.

This story is breaking and will be updated.