Nigeria's President Muhammadu Buhari has appointed the retired diplomat Ibrahim Gambari as his new chief of staff.

The former senior UN official also served in Mr Buhari's military government in the 1980s.

He replaces Abba Kyari, who died last month from coronavirus.

While Mr Gambari is hugely experienced, the fact that he is 75 years old has led to some criticism of the appointment.

Critics of the 77-year-old president say his own frail heath has had a direct impact on the quality of leadership in Nigeria.