Violence reportedly broke out in Gabon late Wednesday following the re-election of President Ali Bongo, with security forces allegedly attacking the headquarters of the opposition.
Two people were killed and several injured in the attack, opposition leader Jean Ping told Radio France Internationale (RFI).
He said his party's headquarters had been bombarded by helicopters before troops from the presidential guard stormed the building.
Earlier, opposition activists had reportedly broken into the area surrounding the parliament building in the capital Libreville and started a fire, while the home of Deputy Prime Minister Paul Biyoghe-Mba was also set on fire.
The violence came after Bongo won re-election by a narrow margin in the central African nation, extending his family’s 49-year reign.
Bongo received 49.80 per cent of votes in Saturday’s election, RFI reported, closely followed by Ping with 48.23 per cent.
Presidential elections are held in a single round in Gabon, with the candidate with the most votes winning outright.
Ping accused the government of fraud. "This scenario has been repeating itself for the past 50 years," he told RFI. "The opposition always wins the elections, but never takes power."
Almost 60 per cent of 630,000 eligible voters cast their ballot in the nation of roughly 1.7 million people, according to the electoral commission.
To ensure peace and stability after such a tight election result, the European Union demanded the electoral commission make public “the detailed results” of each polling station.
The US State Department released a statement saying it was "deeply concerned regarding unfolding events in Gabon."
It called on the government to release results from each polling station in order to "give the people of Gabon, as well as the international community, confidence the announced vote tallies are accurate."
The US also urged "all security forces to act with both restraint and respect for the human rights of all Gabonese citizens."
The election victory secures Bongo, whose Gabonese Democratic Party has a firm grip on power in the oil-rich nation, a second seven-year term.
The 57-year-old was elected for a first term in disputed 2009 polls following the death of his father Omar Bongo Ondimba, who had ruled Gabon since 1967.
Under Omar Bongo, the former French colony tapped into its new-found oil wealth to become the world's fifth largest oil producer.
However, most of the oil wealth has not trickled down to ordinary people, while critics accuse the Bongo family of corruption and despotism.