ABUJA A Nigerian tribunal on Tuesday rejected opposition demands for a re-run of last year's presidential election, averting a political crisis in Africa's most populous nation.
Umaru Yar'Adua won a landslide victory, but local and international observers said vote-rigging was so rampant that the results were "not credible".
A special five-judge tribunal rejected legal challenges filed by the two main opposition candidates, former army ruler Muhammadu Buhari and former Vice-President Atiku Abubakar.
"Umaru Yar'Adua and Goodluck Jonathan remain the president and vice-president of the Federal Republic of Nigeria," said Judge John Fabiyi at the conclusion of a ruling that took more than three hours to deliver.
Major oil exporter Nigeria, a chaotic country of 140 million people, emerged just nine years ago from decades of coups and army rule. Many politicians had feared that instability would return if Yar'Adua's election was annulled.
The two challengers immediately said they would appeal to the Supreme Court. This could take several more months.
"For us, we have come to the semi-final," Buhari told reporters immediately after the ruling.
The odds for the Supreme Court decision appear heavily stacked in favor of Yar'Adua after the tribunal rejected every single one of the challengers' points.
It said Buhari had failed to prove that violations of the electoral law were substantial enough to invalidate Yar'Adua's victory. It ruled that Abubakar had not been excluded from the poll, as he had alleged, but rather had participated actively.
"It is a very disappointing judgment," said Innocent Chukwuma, head of the homegrown Transition Monitoring Group.
"We had expected the tribunal to go beyond mere technicalities and address the yearnings of Nigerians for fair and credible elections," he said.
But economists said the ruling had strengthened Nigeria's political stability and this would reassure investors.
"We expect the decision to be positive for the performance of Nigerian markets," said Razia Khan, regional head of research for Africa at Standard Chartered Bank in London.
Uncertainty over whether Yar'Adua would finish his four-year term had slowed policy-making and investment decisions, and economists expressed hope the pace of reform would now pick up.
"The key is whether the greater political certainty translates into more effective government. There is not a lot the government can point to after nine months in power," said Graham Stock, Africa strategist at JP Morgan in London.
In a statement after the ruling, Yar'Adua pledged to run "a purposeful and result-oriented administration that will yield tangible and visible benefits for all Nigerians".
He also promised electoral reform to ensure that similar disputes do not arise in future.
Tribunals at state level have cancelled the elections of seven out of 36 state governors who were also elected last April, as well as the elections of the Senate president and dozens of legislators. The rulings cited voting irregularities.