"No one should doubt that we will conduct politics without arms", said Timochenko, who asked for forgiveness from FARC victims.
The agreement to end Latin America's longest-running conflict will turn the FARC guerrillas into a political party fighting at the ballot box instead of the battlefield they have occupied since 1964.
More than a quarter of a million people died and thousands more were displaced by the years of violence.
Kerry congratulated Santos for his efforts to achieve peace, saying, "You've extended your political capital".
FARC which stands for the Revolutionary Armed Forces of Colombia, began as a peasant revolt, became a big player in the cocaine trade and at its strongest had 20,000 fighters.Now it must hand over weapons to the United Nations within 180 days. Polls indicate the deal will be approved by a wide margin despite a campaign led by current Senator and former President Alvaro Uribe, a staunch conservative, to reject the agreement. The State Department lists the FARC as a terror organization.
Despite the positive atmosphere and fanfare taking place at the Cartagena's Convention Center where the accord was signed, former president and outspoken opponent to the agreement, Sen.
The organisation has been listed since June 2002 under the so-called "EU terrorist list", which established a list of persons, groups and entities involved in terrorist acts and subject to restrictive measures.
He says in Cartagena, Colombia, that the USA will be watching whether FARC rebels reintegrate into society, disarm and embrace the terms of reconciliation before making a decision.
The Colombian Government must ensure truth, justice, reparation and guarantees of non-repetition for the victims of the Colombian conflict, urged the Catholic agencies in a statement released today.
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Over the decades, the conflict has drawn in several leftist rebel groups, right-wing paramilitaries and drug gangs.
"What we are signing today is your victory", he said.
Flag of Revolutionary Armed Forces of Colombia.
"We negotiated the best deal possible, the best deal possible which will allow us to have peace".
He concluded by urging Colombians to vote "Yes" in a plebiscite to be held on October 2. While amnesty will be granted to those accused of "political crimes", those accused of war crimes will face trial, BBC reported.
It comes after the government signed a peace deal with the FARC rebel group, a deal four years in the making.
But there were also sporadic protests, including one in Cartagena led by conservative former President Alvaro Uribe, whose decade-long, USA -backed military offensive forced the FARC to the negotiating table.
Kerry told attendees that "anybody can pick up a gun, blow up things, hurt people", but it will not be about positive change.
It was one of many symbolic gestures during the 90-minute ceremony overlooking the colonial ramparts of Cartagena that filled Colombians with hope and optimism for the arduous work ahead implementing a 297-page accord that took four grueling years to negotiate. Many families have been touched by rebel kidnappings and it will take years to heal the wounds from a conflict that claimed 220,000 lives and drove 8 million people from their homes.