Nigeria's Senate President Bukola Saraki has defected to the opposition People's Democratic Party (PDP), in the latest blow to ruling All Progressive Congress (APC) in the run-up to elections next year.

Mr Saraki said the APC had failed to live up to its promises since taking power in 2015, and he had decided to pitch his "political tent elsewhere".

Nigeria’s Ambassador to South Africa, Alhaji Ahmed Ibeto, and Kwara State Governor Abdulfatah Ahmed also announced their defection to the PDP.

These are the latest defections to hit the APC. Last week, nearly 50 lawmakers crossed the floor, resulting in the APC losing its majority in the Senate, the upper chamber of parliament.

There has been intense speculation in Nigeria that the opposition is planning to bring impeachment proceedings against Mr Buhari ahead of elections.

His critics accuse him of mismanaging the economy, and failing to tackle insecurity.

He denies the allegation, and is confident of winning a second term.