Colombia's government and its largest rebel group signed a new, modified peace accord on Saturday following the surprise rejection of an earlier deal by voters in a referendum.

Chief government negotiator Humberto de la Calle and rebel negotiator Luciano Marin, alias Ivan Marquez, signed the deal in Cuba, moving to end to a half-century-long conflict that has claimed more than 220,000 lives.

"I want to congratulate the government and people of Colombia on achieving a revised peace agreement," said U.S. Secretary of State John Kerry in a statement. "President Santos and his negotiating team, those from the 'No' campaign, and other important sectors of Colombian society deserve credit for engaging in a far reaching and respectful national dialogue following the plebiscite."

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"This progress is a testament to the commitment shown by all sides, including those who did not support the original accord, to ending this 52-year conflict and building a just and lasting peace in Colombia," National Security Advisor Susan Rice added.

President Juan Manuel Santos and the Revolutionary Armed Forces of Colombia inked an initial peace deal on Sept. 26 amid international fanfare after more than four years of negotiations. But voters rejected it on Oct. 2 by just 55,000 votes, dealing a stunning setback to Santos who won the Nobel Peace Prize for his efforts to end Colombia's conflict.

Santos immediately began looking for ways to rescue the deal and the sides extended a cease-fire until Dec. 31 to get the modified deal done. The rebels insisted they wouldn't go back to the drawing board and throw out years of arduous negotiations with the government.

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"The meetings with the FARC delegation were intense," said De la Calle. "We worked 15 days and nights to reach this new agreement."

It was unclear if or how the modified deal would be submitted to a referendum.

De La Calle said among the modifications made were related to punishments and justice for participants in the conflict accused of war crimes.  He said the exact details would be released later.

"We are convinced that this accord offers roads to peace that are viable and possible," he said.

Hours earlier, conservative former President Alvaro Uribe, who led the opposition to the original deal, called for the confirmation of the accord to be held up until the victims of the conflict and the deal's opponents could review the text.

Following a meeting with Santos in Colombia, Uribe read a statement to reporters saying he had asked that the "texts to be announced from Havana" not be definitive until they had been reviewed.

Uribe and his supporters had demanded stiffer penalties for rebels who committed war crimes and criticized the promise of a political role for the FARC, a 7,000-strong peasant army that is Latin America's last remaining major insurgency

Opponents of the initial agreement questioned, among other things, that guerrilla leaders involved in crimes against humanity would be spared jail time and allowed to enter political life.