Hundreds backing Gabon's main opposition leader risked sanctions Saturday, gathering to welcome Andre Mba Obame back from 14 months in France after his claim to have won presidential elections.

Obame, leader of the now dissolved National Union (UN) party, is due to arrive at the capital Libreville's Leon Mba airport Saturday evening to a hero's welcome, despite official warnings that this was illegal.

"A dissolved, and therefore unauthorised, party is not allowed to hold rallies. That's the law. Those who are involved obviously risk punishment," said presidential spokesman Alain-Claude Bilie-By-Nze.

His return is a key event in Gabon, which has not had a main opposition figure to President Ali Bongo Ondimba since the death of Pierre Mamboundou, leader of the UPG (Union of the Gabonese People), in October 2011.

Once close to Ali Bongo's father Omar Bongo Ondimba, Obame switched sides after the older Bongo's death in 2009 to form the opposition to the late president's son.

Obame's party was dissolved by authorities in 2011 after he proclaimed himself president in a 2009 election won by Bongo.

Accused of "disturbing public order" and "threatening state authority", for which he risks a prison sentence of between two months and one year, and stripped of his parliamentary immunity, Obame left Gabon for France.

Authorities deny that an increased police presence in the capital in the last few days is linked to the politician's return, which they called a "non-event".

"You cannot reproach state authorities for not maintaining the security of Gabonese and then complain when police are out on intersections", said Bilie-By-Nze.

Though officially dissolved, the UN continues to function and party supporters have mobilised for Obame's return, timed for just a few days before Gabon's independence day on August 17.

In recent days, minibuses have brought people from the province of Woleu-Ntem in the Fang heartlands -- the ethnic group to which Obame belongs -- and hundreds of posters put up around the capital.

The National Union and other opposition groups have demanded a national conference to demand sweeping reforms including the dissolution of Gabon's national assembly and a new constitution. They also want elections in 2013.

According to the presidency, "no conference is needed" as "Gabon is not a country in crisis".

In returning, Obame risks imprisonment if authorities decide to pursue him.

"Mr Mba Obame himself said he was ready to take up his work again. So he is ready to answer a call to justice;" said Bilie-By-Nze.

Last month a combative Obame said he was ready for the fight.

"I left Gabon in a wheelchair, I'll come back on my two legs. People that have said I'm dead and gone had better prepare to fight against my ghost."