The leader of a coup that ousted Gabon's President Ali Bongo will address the nation for the first time as interim president on Monday after a swearing-in ceremony that would appear to solidify the junta's grip on power.

In West and Central Africa's eighth coup in three years, military officers led by General Brice Oligui Nguema seized power on August 30, minutes after an announcement that Bongo had secured a third term in an election - a result they annulled and said was not credible.

Nguema, who the officers have since picked as their official leader, will be sworn in as so-called Transition President at 1000 GMT and give a speech on national television.

The coup, which ended the Bongo family's 56-year dynasty, drew cheering crowds onto the streets of the capital Libreville but condemnation from abroad.

Leaders of the Central African regional bloc ECCAS are due to meet in person on Monday to discuss their response to the ouster. Last week they urged partners led by the United Nations and the African Union to support a rapid return to constitutional order.

The junta has not yet said how long it envisages holding power. On Friday, Nguema said it would proceed "quickly but surely," but cautioned that too much haste could lead to elections that lack credibility.

Gabon's main opposition group, Alternance 2023, which says it is the rightful winner of the August 26 election, has called on the international community to encourage the junta to hand power back to civilians.

Members of Alternance 2023 met Nguema on Sunday for talks, a source in the alliance told Reuters, without sharing further details.

Bongo remains under house arrest. He was elected in 2009, taking over from his late father who came to power in 1967. Opponents say the family did too little to share Gabon's oil and mining wealth with the country's 2.3-million people.