(CNN/AP) — Intelligence reports suggest North Korean leader, Kim Jong Un, has been hospitalized following an unspecified surgery.

A U.S. official with direct knowledge of the report tells CNN he is in “grave danger.” Kim was notably absent from a celebration of his grandfather’s birthday on April 15.

He has not been seen since April 11, when he attended a government meeting.

Details of his condition have not yet been confirmed by U.S. or South Korean officials.

The Associated Press reports that South Korea is looking into the matter.

Officials from South Korea’s Unification Ministry and National Intelligence Service said they couldn’t immediately confirm the report.

The Unification Ministry, which deals with inter-Korean affairs, said it couldn’t confirm another report by Daily NK, which cited anonymous sources to report that Kim was recovering from heart surgery in the capital Pyongyang and that his condition was improving.

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