Yahya Jammeh says he made the decision after a thorough investigation
Gambia's long-time leader has declared he no longer accepts the outcome of last week's election, which he lost to a former Argos security guard.
Defeated president Yahya Jammeh, who had previously vowed to rule for "a billion years", claimed a "thorough investigation" had revealed voting irregularities and demanded fresh elections.
His announcement on state television, which has sparked international condemnation, has plunged the future of the West African country into doubt.
Mr Jammeh had last week conceded defeat to Adama Barrow, who secured 45% of the vote compared to the incumbent's 36%.
There had been celebrations at the prospect of an end to Mr Jammeh's 22-year rule, with many seeing it as a step forward for democracy.
His regime was accused by human rights groups of detaining, torturing and killing political opponents.
But the president has now decided to contest the poll result.
He said: "After a thorough investigation, I have decided to reject the outcome of the recent election.
"I lament serious and unacceptable abnormalities which have reportedly transpired during the electoral process.
"I recommend fresh and transparent elections which will be officiated by a god-fearing and independent electoral commission."
It presents a major challenge to the incoming administration of Mr Barrow, which already faced the problem of dealing with an army that for two decades was loyal to the president.
A political unknown just six months ago, the father of five was thrust into the spotlight as a unity candidate after the jailing of members of the opposition.
Mr Barrow ran an estate agency in the country, but lived in Britain for three-and-a-half years when he was younger, working as a security guard for Argos in London.
The head of Mr Barrow's transition team said the president-elect and his staff were safe.
Mai Ahmad Fatty said: "We are consulting on what to do, but as far as we are concerned, the people have voted.
"We will maintain peace and stability and not let anyone provoke us into violence."
The US State Department has condemned Mr Jammeh's rejection of the results and said it was was a flagrant attempt to undermine a credible election and remain illegitimately in power.
Senegal's foreign minister, Mankeur Ndiaye, has called for an emergency meeting of the UN Security Council and "solemnly" warned Mr Jammeh not to harm Senegal's interests or its citizens in Gambia.
Mr Barrow had been due to take office in late January following a transition period.