By Estelle Shirbon
ABUJA (Reuters) - A Nigerian tribunal upheld the 2007election of President Umaru Yar'Adua on Tuesday, rejectingchallenges from rivals who wanted the vote annulled because ofmassive rigging.
The tribunal in Africa's most populous nation ruled thatopposition candidate Muhammadu Buhari, Yar'Adua's mainopponent, had failed to prove that violations of the electorallaw were substantial enough to invalidate the overall result.
The five-judge tribunal also rejected a challenge broughtby former Vice-President Atiku Abubakar, who came third in theelection that local and international observers said was marredby massive fraud.
"Umaru Yar'Adua and Goodluck Jonathan remain the presidentand vice-president of the Federal Republic of Nigeria," theruling said.
Had the vote been annulled, it could have riskeddestabilising the major oil exporter, which emerged just nineyears ago from decades of army rule and has drawn increasingforeign investor interest.
Yar'Adua's victory was disputed from the moment it wasannounced and doubts over whether he would finish his four-yearterm have delayed policy-making and investment decisions.
Some commentators saw the simple fact that the challengewent through the courts as a positive development on acontinent where disputed elections can lead to violence, asKenya's December 27 vote has done.
"The ultimate winners are our democracy and indeed ourjudicial system, along with millions of Nigerians let down bythe kleptomaniacs who shot or rigged their way into positionsof leadership," wrote Muhammad Al-Ghazali in Daily Trustnewspaper.
The legal battle in Nigeria is still likely to drag onbecause the losing parties can appeal to the Supreme Court.
Official results from the election on April 21 last yeargave Yar'Adua 24.6 million votes, compared with 6.6 million forBuhari and 2.6 million for Abubakar.
A few months ago, most Nigerians would have considered itunthinkable for a court to overturn a presidential election,but multiple annulments of appointments by lower levelappointments have changed that perception.