Colombia's government and FARC rebels signed a controversial revised peace accord Thursday to end their half-century conflict, set to be ratified in Congress despite bitter opposition.

President Juan Manuel Santos and guerrilla leader Rodrigo "Timochenko" Londono signed the new deal with a pen made from a spent bullet, in a low-key ceremony in the capital Bogota.

The original deal -- signed with great fanfare in September -- was rejected by voters in a referendum last month, a shock upset that sent negotiators back to the drawing board.

The new plan bypasses a vote by the Colombian people, against bitter opposition from critics.

They say the revisions are only cosmetic and will still grant impunity for war crimes committed by the Revolutionary Armed Forces of Colombia (FARC).

Santos, who won this year's Nobel Peace Prize for his efforts to end the conflict, said the new deal was better than the original.

"It includes the hopes and observations of the vast majority of Colombians," he said after signing it.

"We all know in our souls that the cost of the armed conflict is too high."

- Fragile ceasefire -

The deal was immediately sent to Congress, where it is expected to pass after being debated next week. Santos and his allies hold a majority in the legislature.

The government and FARC both say they are under pressure for fear that their fragile ceasefire could break down.

A recent wave of alleged assassinations in conflict zones has added to calls to seal a deal fast.

But an aftermath of discord and uncertainty appears likely as opponents promised to keep resisting the peace plan, including with street protests.

"The country has spoken. It has said, 'Yes to peace, but without impunity,'" said top opponent Alvaro Uribe, a conservative ex-president and senator.

"What we have here remains total impunity," he told RCN television.

Speaking later in the Senate, he called for another referendum on some of the contested "basic issues" in the deal.

- Opposition objections -

The government and FARC negotiators' redrafted version of the deal includes concessions from the rebels on issues such as reparations for victims.

But Uribe complains it still ignores key demands, notably on punishing FARC leaders for the killings and kidnappings blamed on the group.

Under the deal, the Marxist rebels would disarm and become a political party.

The deal allows non-custodial sentences for convicted FARC members.

Uribe and his allies demand tougher punishments and say rebel leaders guilty of war crimes should not be allowed to run for office before completing their sentences.

A survey by pollster Datexco published on Wednesday found that 58 percent of people want more revisions to the deal.

- Bypassing voters -

Congress will open a live televised debate on the deal from next Tuesday.

On the streets of Bogota, passerby Overnis Diaz welcomed the agreement.

"We have lived through a war of more than 50 years. We want no more bloodshed," he said.

But another local, Dayanna Gil, said: "It should be approved through a popular vote... We should all have a say."

- Disarmament in months -

Santos said that five days after the deal is approved, the FARC rebels will begin gathering in demobilization zones and will hand over their weapons to the United Nations within five months.

UN Secretary General Ban Ki-moon hailed Thursday's deal.

"The violent incidents that have taken place recently in conflict-affected areas underscore the relevance of many of the commitments contained in the agreement and the urgency of putting them into effect," his spokesman said in a statement.

The Colombian conflict has killed at least 260,000 people and displaced seven million since it erupted in 1964, according to the authorities.

It has drawn in various left- and right-wing armed groups, state forces and gangs.

Recent efforts by the government to start talks with the second-biggest rebel group, the leftist ELN, have failed due to disputes over hostages.

ELN rebels say Colombian army ops threaten talks
Quito (AFP) Nov 25, 2016 - Colombia's ELN rebels said Friday that military operations in one of their strongholds were endangering the life of a hostage and the prospects for stalled peace talks.

The warning came as President Juan Manuel Santos seeks to implement a peace deal signed Thursday with a larger rebel group, the Revolutionary Armed Forces of Colombia (FARC), and revive the aborted talks with the National Liberation Army (ELN).

Planned talks with the ELN broke down last month before they could start after the rebels failed to release hostage ex-congressman Odin Sanchez.

The guerrillas now accuse the army of putting Sanchez's life at risk by increasing operations in the jungle-covered department of Choco in northwestern Colombia, where he is being held.

"The increase in violent confrontations is endangering the process of freeing Odin Sanchez, preventing us from presenting proof he is still alive and putting his life at risk," the ELN said on Twitter.

They suggested that forces hostile to Santos within the army are seeking to "weaken the government and cause the ELN talks to fail."

The government earlier Friday demanded proof from the rebels that Sanchez is still alive.

Sanchez voluntarily went into ELN custody in April to take the place of his brother Patrocinio, who had fallen ill after three years in captivity.

Rumors of his death have swirled in recent days.

Santos won this year's Nobel Peace Prize for his efforts to end Colombia's half-century conflict, which has claimed 260,000 lives.

But tough opposition from hardline critics of both the newly revised FARC deal and the proposed ELN talks has cast uncertainty on the peace process.

FARC wants 'peace alliance' for Colombia 2018 vote
Bogota (AFP) Nov 25, 2016 - Colombia's FARC rebels called Friday for proponents of a controversial peace deal to support a single presidential candidate for elections in 2018, as the guerrillas prepare to turn to politics.

Speaking a day after signing a revised peace accord that has left the country deeply divided, FARC chief Rodrigo "Timochenko" Londono sought to strike an alliance to protect the deal from its opponents.

The proposed coalition would bring together what would once have been unlikely bedfellows: the FARC with President Juan Manuel Santos and his allies.

Timochenko wants them to team up against opponents, led by ex-president Alvaro Uribe, who oppose the deal as too soft on the FARC.

"We have begun calling for a candidacy that gathers together all the aspirations of those who want peace and guarantees the continuity of these accords," Timochenko told a press conference.

"The forces that oppose peace are already campaigning for the elections... so why don't we who want peace start talking now?" he said.

He did not name names, but one person floated as a possible candidate to succeed Santos is the government's chief negotiator in the two-year peace talks, Humberto de la Calle.

Colombia's future is hanging in the balance as Santos approaches the end of his second and final term in 2018.

Santos won this year's Nobel Peace Prize for negotiating a historic accord with the FARC, seeking to end a half-century conflict that has claimed 260,000 lives.

But after Uribe campaigned against the deal as granting impunity to war criminals, voters narrowly rejected it in a referendum last month.

The government and FARC have now signed a revised deal, which they plan to ratify in Congress -- bypassing a second referendum.

But Uribe and his Democratic Center party have vowed to fight it, setting up a heated battle that will likely spill over into the mid-2018 vote.