Colombia's president and the leader of its biggest rebel group have sealed a "definitive ceasefire" after 52 years of war.

President Juan Manuel Santos and Rodrigo Londoño, of the Revolutionary Armed Forces of Colombia, or FARC, signed the historic agreement at a solemn ceremony this Thursday in Havana, Cuba.

The accord — that comes after three years of talks, the last stages of which have been based in Cuba — paves the way for a final peace deal to end a conflict born in the 1960s.

The FARC was just one of many Latin American guerrilla movements inspired by Marxist ideology that formed in the wake of Cuba's revolution in 1959. But as the decades passed, what had begun as a peasant revolt against deep injustices and acute poverty transformed into a cocaine-fueled war that also involved state-backed paramilitaries.

'Let this be the last day of the war'

Over the last half century Colombia's conflict has killed at least 220,000 people, and displaced millions.

"Let this be the last day of the war," said guerrilla leader Londoño, who is usually referred to by his alias Timochenko. "So much blood, devastation, and horror could have been avoided if the voices in favor of dialogue had been heard rather than the voices of fascism."

Prior to this week's historic deal, the two sides had already reached agreements on a number of thorny issues such as land reform and participation by former rebels in Colombia's political life.

"Today we are turning this tragic page of our history," President Santos said at the ceremony. "It will allow us to start healing our wounds and teach our children to never repeat what happened and that the time to live without war has come."

Santos stressed that the deal not only promises an end to confrontations, it also lays down details of the FARC's demobilization as a fighting force.

Thursday's agreement already includes some details of the FARC's future demobilization. It states that the guerrilla must hand over all their weapons within 180 days of the final deal being signed.

Santos, who has staked his political legacy on pushing the peace process with the FARC, has promised that a final peace deal will be signed by July 20.

This is due to lay out the terms for the overall implementation of the whole package of partial accords, and expected to mandate a national plebiscite to ratify them.

"This accord is a big breakthrough, but much remains to be done," said Adam Isacson of the Washington-based Latin America think tank WOLA. "The FARC must work to convince its own ranks of the deal while Santos must convince the Colombian people at large."

The FARC leadership's decision to leave behind armed struggle and transform into conventional politicians leaves Colombia with just one significant guerrilla group — the National Liberation Army, or ELN. The government and the ELN have also begun exploratory peace talks. In the meantime, according to Thursday's agreement, the FARC's weapons are due to be smelted down and transformed into three monuments to peace.