Nigeria's Senate president on Tuesday became the latest senior politician to leave the ruling party, dealing a fresh blow to President Muhammadu Buhari ahead of an election next year.
The opposition People's Democratic Party later said Bukola Saraki, the country's third most senior politician, had defected to rejoin them, becoming the most high-profile figure to leave the All Progressives Congress (APC).
Last week, 16 lawmakers in the upper house left the APC, as did 32 in the lower house and this month an APC faction said it no longer backed Buhari.
The loss of influential figures and divisions in the party peels support from Buhari within powerful patronage networks and among voters ahead of the election scheduled for February 2019.
"After extensive consultations I have decided to take my leave of the All Progressives Congress (APC)," Saraki said on his Twitter feed.
A spokesman for Buhari said the APC would comment later.
The opposition PDP said on Twitter Saraki had "dumped the failed and dysfunctional" APC. The PDP was in power from the start of civilian rule in 1999 until Buhari took office in 2015.
The APC coalition united to unseat Buhari's predecessor Goodluck Jonathan in 2015 but it is now divided between Buhari loyalists and those who say they have been targeted by him.
Saraki's supporters said he had for years been targeted by the presidency. He has been dogged by accusations of misconduct and investigations since taking the post in 2015 with the support of opposition lawmakers but has not been convicted.
Saraki's defection was expected, said Antony Goldman of Nigeria-focused PM Consulting, noting that defections to the APC helped Buhari to defeat Jonathan.
"The challenge now for the opposition will be to overcome factional differences and personal ambitions and find, at this relatively late stage, a credible candidate to challenge President Buhari next February," he said.
Nigeria's main opposition parties earlier in July agreed to form an alliance to field a joint candidate to contest the election.
Buhari said in April he would seek another term and he looks set to receive party approval. Party primaries to choose presidential candidates run from Aug. 18 to Oct. 7.
Divisions in the APC emerged since its conference in June when new party leaders were elected and others saw their hopes of party advancement dashed. All but two of the 16 senators who left the APC last week joined the opposition PDP. As a result, the APC has lost its Senate majority.