By Gerauds Wilfried Obangome
LIBREVILLE (Reuters) - Supporters of Gabon's President Ali Bongo and his chief rival both said on Sunday they were set to win a presidential election that poses the most serious challenge yet to the Bongo family's half-century rule in the tiny, oil-rich nation.
Backers of the president and his main challenger, Jean Ping, also traded accusations of fraud allegedly committed during Saturday's vote, raising the prospect of increased tension in the wake of an uncharacteristically bitter campaign.
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At a large gathering of supporters at his campaign headquarters in the capital, Ping, 73, distributed figures showing him handily beating Bongo.
"The general trends indicate we're the winner of this important presidential election," Ping told backers and reporters. "Despite numerous irregularities ... you have managed to thwart this regime's congenital traps of fraud."
Interior Minister Pacôme Moubelet-Boubeya, who had already warned candidates that giving results before the official declaration was against the law, condemned Ping's announcement.
"The candidate Jean Ping has just carried out an attempt to manipulate the democratic process," he said in a statement distributed late on Sunday.
Official results are expected on Tuesday.
Bongo, 57, who first won election after his father Omar died in 2009 after 42 years in office, has benefited from being the incumbent in a country with a patronage system lubricated by oil largesse.
Gabon's one-round election means the winner simply requires more votes than any other candidate. In 2009, Bongo won with 41.73 percent of the vote.
Addressing Ping's declaration, Bongo warned his rival against pre-empting the result by claiming victory before an official announcement.
"You must not sell the skin of the bear before you've killed him," he said, speaking at one of his campaign offices in Libreville. "In any case, I am confident."
Minutes earlier, his spokesman Alain Claude Bilie By Nzé told journalists that Bongo was leading in five of Gabon's nine provinces.
In comments broadcast overnight on state-owned television, the spokesman went even further, stating that Bongo was poised to win another term in office.
"Even if no figure can or should be given at this stage, we are, in light of information we are receiving, able to say that our candidate ... will claim victory," he said.
Bilie By Nzé also said "massive fraud" had been observed during the vote, particularly in polling stations located in opposition strongholds.
The interior ministry on Sunday acknowledged fraud had been noted in some polling stations. But it offered little detail and said that the process remained "satisfactory and positive".
An oil producer with a population of less than two million, Gabon is one of Africa's richest countries.
However, declining oil output and falling prices have resulted in budget cuts and provided fodder for opposition claims that the average person has struggled under Bongo's leadership. His re-election bid was also hobbled by a series of high-profile defections from the ruling party.
Ping, one of 10 candidates contesting the poll, is a former foreign minister and African Union Commission chairman, who was a close ally of Omar Bongo.
Some opposition supporters have called into question Bongo's Gabonese nationality, claiming he was adopted from eastern Nigeria as a baby, a charge that risks fuelling xenophobic sentiment and which the president denies.
(Additional reporting and writing by Joe Bavier; Editing by Andrew Bolton and Adrian Croft)