The director of the International Atomic Energy Agency says he will not run for another term in office after his contract expires next year.
An agency document, sent to IAEA board members, says Mohamed ElBaradei "is not available for a further term" in office.
The 66-year-old Egyptian became the director of the U.N. agency in 1997. He was awarded the Nobel Peace Prize in 2005.
He has presided over investigations into controversial nuclear activities in Syria, Libya, North Korea and Iran.
The United States has accused ElBaradei of being too lenient with Iran, which the U.S. has accused of working to produce nuclear weapons. Tehran says its nuclear program is peaceful.
Some information for this report was provided by AFP and Reuters.