Gabon's main opposition group, Alternance 2023, has called on the international community to encourage the junta that overthrew President Ali Bongo to hand power back to civilians.
Military officers seized power in a coup on Wednesday minutes after an announcement that Bongo had secured a third term in an election.
They placed him under house arrest and picked General Brice Oligui Nguema as transitional leader.
The junta has said little about its immediate plans after ending the Bongo family's almost six decades in power, a move that drew cheering crowds onto the streets of Libreville.
Bongo had ruled since 2009, taking over from his father when he died after he had been president since 1967.
Opponents say the family did little to share Gabon's oil and mining wealth with its 2.3 million people, with almost a third of them living in poverty.
"We were happy that Ali Bongo was overthrown but ... we hope that the international community will stand up in favour of the Republic and the democratic order in Gabon by asking the military to give back the power to the civilians," Alexandra Pangha, spokesman for Alternance 2023 leader Albert Ondo Ossa told the BBC.
Alternance 2023 has said it wanted a full vote count from Tuesday's election which it said would show Ondo Ossa had won.
Gabon's election commission said Bongo had been re-elected with 64 per cent of the vote, while Ondo Ossa secured almost 31 per cent.
Pangha said the opposition hoped to get an invitation from the junta to discuss the Central African country's transition plan and return to the republican order but said it had not received anything yet.
Nguema, leader of the officers behind the coup, is expected to be sworn in as transitional president on Monday, the junta has said.
He will also give his first presidential address.
"We think it's absurd for the putschists to swear in on Monday," Pangha said.
The African Union's Peace and Security Council demanded on Thursday that the military refrain from any interference in the political process and called for fair and transparent elections.
France, Gabon's former colonial ruler, and other Western powers have condemned the military takeover.