(Adds Uribe comment, paragraphs 13-14)
By Helen Murphy
BOGOTA, June 16 (Reuters) - President Juan Manuel Santos vowed to bring peace to Colombia after winning re-election on Sunday, telling Marxist rebels his victory shows that voters demand an end to five decades of war.
Santos, a center-rightist who has staked his reputation on securing a peace deal with the Revolutionary Armed Forces of Colombia (FARC), won almost 51 percent support in the runoff election on Sunday. His right-wing rival Oscar Ivan Zuluaga trailed with 45 percent.
The election divided Colombia between voters who support a deal to end Latin America's longest-running insurgency and Zuluaga's backers who want to force the rebels into a battlefield surrender.
"This is the end of more than 50 years of violence and the start of a new Colombia," Santos said after his election victory, holding up a hand daubed with the word "peace" and wearing a trademark pin of a white dove on his lapel. "A Colombia at peace with itself."
Santos opened talks with the FARC in late 2012. The conflict has killed over 200,000 people and forced millions more from their homes.
Last week, Santos also revealed preliminary talks with a smaller rebel group, the National Liberation Army (ELN), and he said on Sunday the Colombian people were now insisting on peace.
"The demand is not just for the government. Today's message is for the FARC and the ELN and it's a clear message - this is the end," the center-right president said surrounded by family.
He will start his second four-year term on Aug. 7.
During a bitter campaign, Santos faced a barrage of criticism from Zuluaga and his mentor, former President Alvaro Uribe. They played to the outrage felt by millions of Colombians that FARC leaders could escape prison time and even hold public office as part of a negotiated settlement.
Zuluaga's strong support in the election shows how tough it will be for Santos to win the nation's approval in a future referendum if a peace deal is signed and for it to pass through Congress.
And Uribe will be a formidable foe after being voted into the Senate in March. (For more on the vote, see )
The former president on Monday denounced what he said were incidents of vote-buying, accusing the Santos campaign of abuse of power and fraud.
"It is hard to find a moment in the history of Colombia when there has been this amount of illegal money, this abuse of power by the President-elect and this fraud," he said.
'PREPARED FOR PEACE'
Santos, the son of one of the country's most influential families and a Harvard-educated economist, says he began to dream of leading Colombia toward peace two decades ago.
Learning from the mistakes of previous attempts to end the war, Santos said he promised himself he would not allow the rebels to strengthen their ranks, build up their war chests or take the upper hand over the government.
"You don't improvise with peace building," Santos told Reuters in a recent interview. "I've spent 20 years thinking about this opportunity. I'm prepared, I'm well advised and hopefully this process will be irreversible."
Agreements have already been reached with the FARC on three items on a five-point agenda, including land reform and the rebels' withdrawal from drug trafficking.
A key question is whether the rebels will be more stubborn at the negotiating table after recent advances, especially now that they no longer have to worry about a Zuluaga victory.
Responsible as defense minister under Uribe for operations that killed senior FARC leaders, Santos insists there will be no impunity for serious crimes, but also says it is unrealistic to probe 50 years of atrocities.
As his supporters raised cut-out figures of white doves on Sunday, Santos recognized that achieving peace will not be easy and thanked those voters from the left who rallied around him in the election runoff.
"This was a triumph for millions of compatriots who support a dream we share. They voted to change fear for hope." (Editing by Kieran Murray and W Simon)