* UN, US and France reject Gbagbo victory, back Ouattara
* Ouattara's opposition camp warns of return to civil war
* Cocoa futures rise more than two percent
(Adds armed forces chief)
By Tim Cocks and David Lewis
ABIDJAN, Dec 3 (Reuters) - Ivory Coast's armed forces chief pledged allegiance to President Laurent Gbagbo on Friday, after the nation's top legal body declared the incumbent the winner of a contested election, a move that has sparked fears of unrest.
U.S. President Barack Obama earlier led international calls for Gbagbo to accept defeat in last month's presidential run-off, rejecting a Constitutional Council ruling that overturned provisional results and handed victory to Gbagbo.
"We came to greet the president of the republic, to give him our respect, reiterate our readiness and allegiance and tell him that we are ready to carry out any mission that he wants to give us," General Philippe Mangou said on state television after being shown visiting Gbagbo with other senior officers.
Disagreement over the outcome has raised the risk of renewed bloodshed in the world's top cocoa producer nation, where the much-delayed election was meant to heal the wounds of a 2002-03 civil war but instead has reopened them.
Gbagbo's rival, ex-IMF official Alassane Ouattara claimed the win from the Nov. 28 run-off vote, and was quickly endorsed by rebels who fought against Gbagbo in the war and who still control much of the country's north.
Residents reported gunfire after nightfall in the Abobo neighbourhood and security forces used teargas to disperse protesting Ouattara supporters there and elsewhere in the main city of Abidjan. A Reuters reporter saw the Republican Guard deployed in the town centre around Gbagbo's palace.
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In a statement, U.N. spokesman Martin Nesirky said U.N. Secretary-General Ban Ki-moon backed overturned provisional results that showed Ouattara had won with 54.1 percent of the vote -- taking what U.N. diplomats in New York said was an unusually tough stance on the issue.
"The Secretary-General congratulates Mr. Alassane Ouattara ... on his election and calls upon the President-elect to work towards lasting peace, stability and reconciliation in Cote d'Ivoire (Ivory Coast)," the U.N.'s Nesirky said.
"The Secretary-General also calls upon President Laurent Gbagbo to do his part for the good of the country and to cooperate in a smooth political transition," he added.
Obama and French President Nicolas Sarkozy, whose country is the former colonial power in Ivory Coast, later joined Ban in recognising Ouattara as the winner of the election.
Earlier, Ivory Coast's Constitutional Council -- led by a staunch Gbagbo ally -- upheld the incumbent's complaints that the vote had been rigged by pro-Ouattara rebels in the north and declared him the re-elected president.
A Gbagbo advisor accused the United Nations of meddling in Ivory Coast's internal affairs and threatened to expel the head of the U.N. peacekeeping mission there.
The local U.N. mission is required under existing peace accords to sign off on the outcome before it can be validated.
The U.N. endorsement of Ouattara raises numerous questions about how far the world body, which has some 10,000 peacekeepers and police in the country, is ready to go if Gbagbo insists on remaining in power despite huge international pressure.
The uncertainty propelled cocoa futures higher, with the March contract ending 36 pounds higher at 1,959 pounds a tonne. However some analysts suggested the move was overdone and noted that even during the war, cocoa came out of the country.
THREAT OF CONFLICT
In a statement issued from their stronghold in the northern town of Bouake, the rebel group New Forces said they backed Ouattara. Rebels in the north had in principle agreed to disarm as part of the peace process but they remain in control of the north and many have not given up their weapons.
Allies of Ouattara warned earlier of a possible return to war if the Constitutional Council, headed by Gbagbo party ally Paul Yao N'dre, overturned the provisional result -- a move he promptly announced minutes later on state television.
"If Yao N'Dre does it he will be to blame for the next war in Ivory Coast," said Ouattara aide Jeannot Ahoussou.
"This is typical of Gbagbo ... Unfortunately, it puts the country back into a potential conflict zone," Tara O'Connor of London-based Africa Risk Consulting said of Gbagbo's perceived reluctance to leave office.
O'Connor suggested the United Nations could push for "targeted sanctions" on his leadership -- measures that can include travel bans or foreign assets freezes on individuals and which have been used on rogue leaders with varying success.
"The next thing will be to watch how many African leaders come out to congratulate Gbagbo on his win," said a diplomat in Abidjan. "Sanctions are definitely on the cards. They could move very quickly."
Ivory Coast's ${esc.dollar}2.3 billion Eurobond, a bellwether of recovery hopes for what used to be one of the region's star performing economies, yielded 10.97 percent on Friday, up from pre-vote levels of below 10 percent. (Additional reporting by Ange Aboa in Bouake and Loucoumane Coulibaly in Abidjan; Louis Charbonneau at the United Nations; Nigel Hunt in London and Richard Valdmanis in Dakar; writing by Mark John; Editing by Richard Valdmanis and Jon Boyle)
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