Colombia's government and Marxist rebels signed a revised peace deal on Thursday to end Latin America's longest running conflict, but implementing the new accord faces an uphill battle amid critical opposition in the divided country.

Colombian President Juan Manuel Santos and FARC rebel leader Rodrigo "Timochenko" Londono signed the deal - the second in nearly two months - in a low key ceremony in Bogota after voters narrowly rejected a previous deal in a referendum on October 2.

"I invite you to leave decades of violence forever in the past, to unite for all of us, for Colombia, for this dear nation, and to work together for reconciliation around shared ideals of peace," Santos said.

Santos had vowed to reach a new peace deal as soon as possible after the failed referendum, warning that a drawn out process threatened to upend more than four years of tough talks and throw the country back into violence.

In a rush to seal the deal, Santos will take it to Congress for debate next week, where it is likely to pass. Santos and his allies hold a majority in the legislature.

Critics of the first deal said it was too easy on FARC, and they have voiced similar concerns over the revised plan. After the referendum was defeated, Santos reached out to the backers of the "No" vote and took in their proposals for changes. The government and FARC then met in Cuba to integrate the suggestions of those opposed to a revised agreement deal. 

In the end, the new 310-page accord introduced nearly 50 revisions to appeased critics led by senator and former hard-line president Alvaro Uribe. Among other things, the revised accord changes some provisions of the transitional justice plank of the deal, provides assurances on respect of private property and commits rebels to use funds gained from drug trafficking for reparations of victims.

The revised accord does not, however, address a key demand from Uribe for FARC leaders and rebels to be banned from politics and face jail time for crimes. Uribe also wanted guarantees for the police and military who may face trial over crimes committed during the conflict.

For FARC, such any prohibition from politics was always a deal breaker for a peace process meant for them to put down their guns, and struggle instead at the ballot box.

"It is very important Colombians understand that the reason for all peace processes in the world is precisely that rebels lay down arms and can participate in legal politics," Santos said earlier this month in a televised address after government and rebel negotiators had agreed to the revised accord in Cuba.

FARC is detested by many Colombians for drug trafficking, kidnappings and running a decades-long insurgency. The lack of universal public support and opposition criticism may threaten a peace deal designed to heal wounds and silence the guns.

Uribe's Democratic Center party may boycott the debate in Congress next week to ratify the agreement, saying the constitution is being violated. They have also called for protests against what they described as a "blow against democracy" for Santos' refusal to take the new accord to another referendum.

"The government preferred to impose itself in a way that divides Colombians instead of a national pact that would bring us together," the Democratic Center party said in a statement Wednesday.

The political cleavages over the deal come amid a worrying spike of attacks that have left dozens of community and land rights activists being killed since September. Separately, two FARC fighters were killed last week in a clash with the army despite a ceasefire in effect since August.

In a failed peace bid in the 1980s, right-wing paramilitaries with ties to the state, landowners and businessmen, killed thousands of former guerrillas, labor activists and communists. In the later phases of the conflict, right-wing paramilitaries have been heavily involved in drug trafficking, human rights abuses and atrocities.

There is also concern over demobilization and reintegration. Under the deal some 8,000 FARC fighters will lay down their guns at UN designation sites, but there is worry some may join criminal drug gangs or the smaller left wing National Liberation Army.

At least 220,000 people have died and some 8 million have been displaced in 52 years of conflict.

cw/kl (AFP, AP, Reuters)