Gabon's opposition leader has lodged a challenge to the presidential election result at the constitutional court.
Defeated presidential candidate Jean Ping has complained of fraud, pointing out that in one province incumbent Ali Bongo won 95% of the vote.
Former African Union chair Mr Ping lost the election by less than 6,000 votes.
The European Union has said there were "clear anomalies" in last month's poll - charges denied by Mr Bongo, who in turn accused Mr Ping of fraud.
The lawsuit was filed on the final day allowed for legal challenges to the 27 August election.
The official election result, announced on 31 August, gave Mr Bongo a second seven-year term with 49.8% of the vote to Mr Ping's 48.2%.
Mr Ping criticised results in Mr Bongo's home province of Haut-Ogooue, where turnout was 99.93% and 95% of votes were for the president.
Turnout in the other provinces was between 45% and 71%, according to Gabon's interior ministry.
Is it worth challenging presidential election results? By Damian Zane, BBC News
A court has never overturned a presidential election result in Africa, according to Robert Gerenge, head of special programmes at the Electoral Institute for Sustainable Democracy in Africa.
In the past year, losing candidates in Uganda and Zambia have failed in their legal efforts, although that it is not to say all elections are rigged.
In Zambia, a technicality stopped Hakainde Hichilema's attempt to get last month's presidential election result changed. He ran out of time to present his case.
Uganda's supreme court in March dismissed Amama Mbabazi's challenge saying that while there were issues, they did not affect the final result.
This ruling had a precedent across the continent.
Following Nigeria's 2007 election, the legal process took 20 months before the courts had a final answer.
The supreme court said despite irregularities, there was no proof that they altered the outcome.
In Zimbabwe, Morgan Tsvangirai initially went to court in 2013 to challenge the re-election of President Robert Mugabe. But he dropped the case, saying that the president had stopped him from getting a fair hearing.
In general there are three types of situations, Mr Gerenge says:
- There is no faith in the legal process so opposition supporters take to the streets rather than the court
- Losing candidates go to court under diplomatic pressure even though they have no faith in the outcome
- Losing candidates have faith that the judges will be impartial
On Monday Gabonese Justice Minister Seraphim Moundounga resigned in protest.
The EU has also questioned the legitimacy of the election results.
But Mr Bongo retaliated, telling France's RTL radio "some of the EU observers overstepped their mission".
When the election results were announced people took to the street in protest.
The Gabonese authorities say three people have died and 105 have been injured following violent clashes and more than 800 arrests.
Mr Ping puts the death toll higher - saying dozens of his supporters have been killed and that a presidential guard helicopter bombed his headquarters.
Gabon election: Bongo v Ping
- Mr Bongo took office in 2009 after an election marred by violence
- He succeeding his father Omar Bongo who had come to power in 1967 and was Africa's longest serving leader
- Veteran diplomat Mr Ping had served as chair of the African Union
- He had been a close ally of Omar Bongo and had been his foreign minister
- He had two children with Omar Bongo's daughter, Pascaline