OSLO (AFP/REUTERS) - Colombia's President Juan Manuel Santos has won the 2016 Nobel Peace Prize, in a surprise decision unveiled on Friday (Oct 7) by a five-member Norwegian committee as the annual Nobel prize-giving week reaches its peak.

It comes as Colombians voted "No" to an agreement he signed with Marxist rebels to end 52 years of war. Mr Santos has promised to revive a peace plan even though Colombians, in a referendum on Sunday, narrowly rejected the accord. Many voters reckoned it was too lenient on the FARC guerrillas.

"The Norwegian Nobel Committee has decided to award the Nobel Peace Prize for 2016 to Colombian President Juan Manuel Santos for his resolute efforts to bring the country's more than 50-year-long civil war to an end," said committee chairman Kaci Kullmann Five.

"The award should also be seen as a tribute to the Colombian people," she said when announcing the prize. Voters did not say 'No' to peace but to the agreement," she said.

The award pointedly excluded FARC guerrilla leader Rodrigo Londono, better known by his nom de guerre Timochenko, who signed the deal with Mr Santos. Some Nobel watchers had taken Colombia off their lists of favourites after the referendum "No".

"The fact that a majority of the voters said 'No' to the peace accord does not necessarily mean that the peace process is dead," the committee said. "This makes it even more important that the parties, headed by President Santos and FARC guerilla leader Rodrigo Londoño, continue to respect the ceasefire.

"The Norwegian Nobel Committee emphasises the importance of the fact that President Santos is now inviting all parties to participate in a broad-based national dialogue aimed at advancing the peace process.

"It's a message of hope for my country and for peace in Colombia," the country's ambassador to Norway, Mr Alvaro Sandoval Bernal, told Norwegian broadcaster TV2. "It reiterates that there is hope for the peace process in Colombia."

Asked why Timochenko was left out, Ms Five said Mr Santos had been central to the process: "President Santos has been taking the very first and historic initiative. There have been other tries, but this time he went all-in as leader of the government with a strong will to reach a result... That's why we have put the emphasis on the president."

She declined to elaborate on Timochenko's role. "We never comment on those who do not receive a reward."

Mr Santos said the award would further help the peace process in the Latin American country, the secretary of the Norwegian Nobel Committee said on Friday.

"He was overwhelmed. He was very grateful. He said it was of invaluable importance to further the peace process in Colombia," Mr Olav Njoelstad told Norwegian state broadcaster NRK after having spoken to the Colombian leader by phone.

"The message is that we have to persevere and reach the end of this war. We are very, very close, we just need to push a bit further," he also said in an interview with the Nobel Foundation. "This (prize) is going to be a great stimulus to reach that end and to start the construction of peace in Colombia."

Mr Santos is the first Latin American to receive the peace prize since indigenous rights campaigner Rigoberta Menchu of Guatemala won in 1992, and is the second Colombian after writer Gabriel Garcia Marquez, who won the literature prize in 1982.

The Peace Prize is the only one of six awards to be presented in Oslo and the one which traditionally garners the greatest attention. Worth 8 million Swedish krona (S$1.27 million), it will be presented in Oslo on Dec 10.

Swedish inventor and scholar Alfred Nobel created the prizes in his 1895 testament, stipulating that his fortune was to be placed in a fund destined to honour "those who, during the preceding year, shall have conferred the greatest benefit on mankind".

The peace prize should go "to the person who shall have done the most or the best work for fraternity between nations, for the abolition or reduction of standing armies and for the holding and promotion of peace congresses", his will said.

With a record 376 nominations considered, experts were far from unanimous over who the committee would choose.

In an illustration of just how difficult it is to call, last year's prize went to four Tunisian groups who were instrumental in the country's transition to democracy - none of whom had been mentioned in any of the pre-announcement speculation.

The Syrian rescuers risking all to save war-hit civilians and the brokers of Iran's nuclear deal were also among the contenders for the peace prize.

Experts, online betting sites and commentators had thought they were on to a sure thing with Mr Santos and Timochenko widely seen as frontrunners after signing a deal to end the civil war.

But they were suddenly forced to rethink after voters in Colombia rejected the agreement between their government and the Revolutionary Armed Forces of Colombia (FARC) rebels in an Oct 2 referendum.

That threw the prestigious prize wide open again.

The prize comes as Colombia teeters between war and peace. Mr Santos and the FARC have been left scrambling to save their peace accord - the product of nearly four years of negotiations - after right-wing hardliners led the successful campaign to vote against it.

The leader of the "No" camp, former president Alvaro Uribe, argued the deal offered the rebels impunity for their crimes and would put Colombia on the path of "Castro-Chavismo" - a reference to the far-left governments of Cuba and Venezuela.

Mr Santos, who has staked his legacy on making peace, has warned that the country is now in a "very dangerous limbo".

He said the army would halt its ceasefire with the FARC at the end of the month if no solution is found - though he later said the deadline could be extended.

The opposition wants Mr Santos to renegotiate a tougher deal with the rebels. FARC leaders have vowed they are committed to making peace, but it is unclear whether they will be able to sell a new deal to the rank and file.

In the meantime, they have ordered their fighters back to "secure sites".

FARC commander Pastor Alape said on Twitter that the order aimed to avoid "provocations" from opponents of the peace deal.

The Colombia conflict has killed more than 260,000 people and left 45,000 missing over five decades, drawing in several leftist guerilla groups, right-wing paramilitaries and drug gangs. The FARC, the oldest and largest rebel group, was to relaunch as a political party under the deal.