Gabonese opposition leader Jean Ping has said a constitution court ruling which upheld President Ali Bongo's election victory was "unjust".
Mr Ping called for his supporters to "remain vigilant and mobilised". There have been concerns about violent protests following the court ruling.
To ease tension Mr Bongo offered to include opposition members in his cabinet.
He came to power in 2009 when his father died after ruling for 42 years.
President Bongo says he is now seeking to form a new government.
"Respect" for Gabonese
Speaking to supporters in the capital Libreville, Mr Ping sought to ensure supporters that the Gabonese people would be "respected" and that "2016 will not be 2009".
Mr Ping had asked the court to re-examine results in the Haut-Ogooue province where Mr Bongo won 95% of the vote on a turnout of 99.9%
But the court threw out copies of tally sheets that Mr Ping had presented as evidence, saying they had not been verified.
Mr Ping had warned that Gabon could face serious instability if the court rejected his appeal for a recount in that province.
James Copnall, Africa Editor
Jean Ping appears to be in no mood to back down.
The opposition leader said the constitutional court was biased. But he's not the only one to criticise the electoral process: the European Union says the Gabonese have the right to question the election's integrity.
So far there has been no protests.
This time round the security forces have been very evident on the streets of the capital Libreville and elsewhere, and most people seem to be staying indoors.
In an interview with Reuters on Saturday Mr Bongo called for political dialogue.
"I look forward to inviting members of all political parties to join our efforts and come with us to the cabinet.
"We don't need international mediation. Among Gabonese, we know how to talk to each other."
The government has said it would hold opposition leader Jean Ping responsible if clashes erupted following the ruling.
President Bongo won August's election by just 6,000 votes but the opposition says the poll was rigged. Election results on 27 August sparked days of deadly violence.
Correspondents say residents of Libreville were stockpiling food ahead of the court ruling. There were long queues at banks and supermarkets on Friday and the French embassy told its citizens to stay indoors.
The court partially changed the results of the bitterly-fought election, cancelling votes from 21 stations over irregularities. This boosted President Bongo margin of victory from 49.85% to 50.66%.
Mr Ping won 47.24% of the vote.