The spokesman's statement circulated on Thursday shortly after a letter from Buhari was read out in the upper house of parliament, saying the 74-year-old former military ruler would go on medical leave.

"While away the vice president, Yemi Osinbajo, will perform the functions of the Office of the President," the spokesman, Femi Adesina, said in his statement. "During the vacation, the president will also undergo routine medical check-ups."

Neither the spokesman's statement nor Buhari's letter gave any details on what medical issue led the president to take leave.

Buhari flew to London for a 10-day holiday in June 2016, during which received treatment for a persistent ear infection, officials said.