A UN representative told Gabon's military leader the UN institutions stood ready to support the country as it transitions back to constitutional order following a coup that ended the Bongo family's 56 years of dynastic autocracy.

Army officers seized power on August 30, annulling an election minutes after an announcement that President Ali Bongo had won, which they said was not credible. Bongo, in power since 2009, had succeeded his father Omar Bongo, who ruled for 42 years.

The coup was greeted with scenes of jubilation in the capital Libreville and on September 4 General Brice Oligui Nguema was sworn in by judges as interim president, promising free and fair elections, but giving no timetable for organising them.

Abdou Abarry, Special Representative of the UN Secretary General in Central Africa, met Nguema in Libreville on Wednesday and told him that the UN would assist the country as it made a fresh start.

"Once we know the roadmap, the timetable, once a government will have been appointed, our different agencies will make the necessary contacts and continue to support Gabon," he said after the meeting, in remarks broadcast on Gabon 24 TV.

The coup in Gabon, an oil-producing country of 2.3-million, was the eighth in three years in West and Central Africa, though it has been playing out very differently from the most recent other army takeover, in Niger.

Unlike Niger, Gabon has not seen an outpouring of anti-French, pro-Russian sentiment, and the generals in charge in Libreville have appeared open to dialogue with international organisations which their counterparts in Niamey have shunned.

The Central African regional bloc, ECCAS, suspended Gabon on Monday but sent the president of Central African Republic, Faustin-Archange Touadera, as its representative to meet Nguema.

Touadera told reporters he had also met Ali Bongo, with Nguema's permission. He did not disclose any details about Bongo's circumstances or state of mind, saying only that the meeting had been fruitful.

Bongo had been under house arrest after the coup, but the junta said in a statement on Wednesday that he was now free and could travel abroad for medical checks if he so wished.