Sudanese President Omar al-Bashir has decided not to take up an invitation from Saudi Arabia to attend an Islamic summit at which US President Donald Trump will be guest of honour.
Sudan had said it was looking forward to improving US ties at the event.
Saudi Arabia is the first stop on Mr Trump's first foreign tour.
A statement from Mr Bashir's office said the president had apologised to King Salman of Saudi Arabia for being unable to attend the Riyadh summit. No further explanation was given.
Minister of State Taha al-Hussein will represent him.