Minutes after Taiwan President Mr Chen Shui-bian won a razor-thin election, opposition candidate Mr Lien Chan said the poll was unfair and called for the result to be declared invalid.
A day after surviving an assassination attempt, Mr Chen won by just 29,518 out of 12.9 million votes cast, in the closest presidential election in the island's history.
"We want to raise a motion to declare the election invalid. We ask the central election commission to seize and seal all ballot boxes," Mr Lien said.
Details of the assassination attempt on Mr Chen while campaigning on the eve of the vote needed to be clarified, he said.
Police have made no arrest since assailants fired at least two shots on Mr Chen and his running mate, Vice President Annette Lu.
"Up to now, we have not had a clear explanation of the truth of yesterday's shooting. Its impact on this election needs no words, and its impact was direct. The doubts surrounding it give us one common impression - this is an unfair election," Mr Lien said.
He also attacked Mr Chen and his Democratic Progressive Party in what has been an acrimonious campaign.
"There are too many suspicions. Not one, but a series of actions that have created a cloud of suspicion," he said in reference to the shooting.
The result is likely to anger China, which considers Taiwan a breakaway province that must be reunited by force if necessary and opposes the pro-independence policies of Mr Chen., who espouses an aggressive policy of establishing Taiwanese independence. Mr Lien favours a more conciliatory approach.
Agencies