Colombians are set to decide whether or not to support a historic peace deal with the country's largest rebel group to end five decades of fighting.

Polls taken before Sunday's referendum - in which voters will be asked if they want to ratify or reject the deal with the Revolutionary Armed Forces of Colombia, known as FARC - show the "yes" side is favoured by an almost two-to-one margin.

But the Colombian government is not taking victory for granted amid a highly polarised campaign that has exposed how steep a challenge it faces implementing the 297-page accord and bringing about real reconciliation.

For the referendum to be ratified, at least 13 percent of the electorate, or 4.5 million voters, must cast "yes" ballots.

Forgiveness key to Colombia peace deal's future

Turnout is expected to be low, no higher than the 40 percent seen in recent congressional elections, a sign to some analysts that Colombians enthusiasm for implementing the ambitious accord is lacking.

The opposition, led by powerful ex-President Alvaro Uribe, argues the government is appeasing FARC and setting a bad example that criminal gangs will seize on.

Apologies for massacres

But FARC officials in recent days have made an effort to show their commitment to peace is real.

Twice this week leaders of the group traveled to areas hard hit by the violence to apologise for massacres committed by their troops in the course of the conflict, and to discuss with communities how they can compensate victims.

On Saturday, in the presence of United Nations observers, they voluntarily destroyed 620kg of grenades and light explosives.

They also said they would compensate victims with financial resources and land holdings accumulated during the war.

Only if it is ratified will the FARC's roughly 7,000 fighters begin moving to 27 concentration zones where over six months they will gradually turn over their weapons to UN observers and prepare for their reintegration into civilian life.

Colombia's long road to peace

Under the accord, FARC - which began as a peasant revolt in 1964 - can compete in the 2018 presidential and legislative elections and has 10 unelected congressional seats guaranteed through 2026.

While the number of seats will not be enough to sway legislation, some Colombians are still outraged.

"The president has given the guerrillas the ability to be in government. He's sold out the country," said 66-year-old Bogota housewife Fanny Castro, whose son-in-law is in the army.

"We have to vote no or we'll have the guerrillas on top of us."

For decades, FARC bankrolled the longest-running conflict in the Americas through kidnapping and extortion, spreading a sense of terror that left few Colombians unaffected.

The conflict claimed more than 220,000 lives and displaced millions of people.

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Source: Agencies