Nearly a dozen soldiers took to state television and said they were overturning the presidential election and called for calm among the population.
We reaffirm our commitment to respecting Gabon's commitments to the national and international community," said a spokesperson for the group.
The soldiers on television were comprised of members from the gendarme, the republican guard and other factions of the security forces.
Gabon President Ali Bongo Ondimba, 64, was seeking a third term in elections this weekend that could extend his family's 55-year political dynasty.
He served two terms since coming to power in 2009 after the death of his father, Omar Bongo, who ruled the country for 41 years.
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There was concern of violence before the election due to deep-seated grievances among the population of some 800,000 people. Nearly 40 per cent of Gabonese ages 15-24 were out of work in 2020, according to the World Bank.
After last week's vote, the Central African nation's Communications Minister, Rodrigue Mboumba Bissawou, said on state television that there would a nightly curfew from 7 pm to 6 am.
He said internet access was being restricted indefinitely as there had been calls for violence and the spreading of disinformation.
Every vote held in Gabon since the country's return to a multi-party system in 1990 has ended in violence.
Clashes between government forces and protesters following the 2016 election killed four people, according to official figures. The opposition said the death toll was far higher.
In anticipation of post-electoral violence, many people in the capital went to visit family in other parts of the country or left Gabon altogether. Others stockpiled food or bolstered security in their homes.