"In the same way that I accepted the results faithfully believing that the Independent Electoral Commission was independent and honest and reliable, I hereby reject the results in totality," he said yesterday in a statement broadcast on state television.
"Let me repeat: I will not accept the results based on what has happened," he said, condemning "unacceptable errors" on the part of electoral authorities and calling for a new vote.
Jammeh pointed to an accounting error, identified by the IEC, which awarded victory to his opponent Adama Barrow but with a slimmer margin than initially announced.
Jammeh claimed "investigations" had revealed that numerous voters had not been able to cast their ballots.
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"This is the most dubious election we ever had in the history of this country," he said.
"We will go back to the polls because I want to make sure every Gambian votes under an electoral commission that is impartial, independent, neutral and free from foreign influence," he said, adding that he would not tolerate any street protests over his decision.
On December 2, Jammeh made a magnanimous concession speech on television and promised -- to general shock and surprise -- a peaceful and swift handover of power to President-elect Barrow.
On Thursday, Barrow vowed to set up a South Africa-style truth commission and said that the country's chief of defence staff had called to pledge the military's backing.
But pressure to prosecute Jammeh and top figures in his administration, who have been accused of widespread human rights violations, is one of the key challenges facing the new government.
Dozens of opposition activists who had been detained since April for holding protests were granted bail this week, with the lawyer noting they were members of the United Democratic Party (UDP), of which Barrow was the presidential candidate.
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