A roller-coaster fortnight for Colombian President Juan Manuel Santos — who signed a historic agreement to end a half-century-old guerrilla war only to see it rejected by voters — ended in euphoria Friday when he was awarded the 2016 Nobel Peace Prize.

Santos staked his presidency on making peace with the Revolutionary Armed Forces of Colombia, known as FARC, which has required four tough years of negotiations in Havana, Cuba, and driven down his job-approval ratings. But the effort produced an agreement that would allow the leftist guerrillas to disarm and form a political party.

In its citation, the Norwegian Nobel committee praised Santos "for his resolute efforts to bring the country's more than 50-year-long civil war to an end."

A supporter of the 'yes' vote cries after the nation voted 'no' in a referendum on a peace deal between the government and Revolutionary Armed Forces of Colombia (FARC). It was a lifeline for Santos who is scrambling to salvage the peace process in the wake of last Sunday's binding referendum in which voters rejected the deal by a razor-thin margin.

That shocking outcome — the polls predicted the "yes" vote would win handily — has forced Santos to consider demands from the political opposition to make the accord much tougher on the FARC. The Nobel Prize now puts very public pressure on all sides to find a peaceful solution.

In an early morning phone call in which he received the news, Santos told the Nobel committee: "The message is we have to persevere until we reach the end of this war. We are very, very close. We just need to push a bit further, to persevere, and this is going to be a great stimulus to reach that end."

Adam Isacson of the Washington Office on Latin America says the Nobel can loom large in such cases. He pointed out that winning the 1987 Nobel Peace Prize bolstered Costa Rican President Oscar Arias in his efforts to end civil wars in Central America in the face of strong resistance from the Reagan administration in the U.S.

FARC commander Rodrigo Londono was overlooked by the Nobel committee but congratulated Santos, saying via Twitter: "The only prize we aspire to is peace with social justice for Colombia."

'Hope of a just peace'

Instead of recognizing Londono, the committee chose to highlight those impacted by the war. Some 220,000 people have been killed, legions have been maimed by landmines and nearly eight million have been uprooted from their homes.

Thus, the committee said its decision was also "a tribute to the Colombian people who, despite great hardships and abuses, have not given up hope of a just peace … This tribute is paid, not least, to the representatives of the countless victims of the civil war."

Some live in former FARC strongholds like the southern town of San Vicente del Caguan. Standing in line at a government centre for war victims, cattle rancher Edelberto Alvarez said FARC rebels killed two of his sons because they had refused to give the guerrillas extortion payments.

He said he hopes Santos uses the Nobel to drag the peace process across the finish line.

Santos, left, and Marxist rebel leader Rodrigo Londono shake hands on Sept. 26 after signing an accord they hoped would end a half-century war. (Reuters) "We have faith in God that there will be a solution," Alvarez said. "That is what everyone wants."

Santos, 65, becomes only the second Colombian to win a Nobel following novelist Gabriel Garcia Marquez, who was honoured for literature in 1982.

Santos joined the Colombian navy straight out of high school, an odd choice as he hails from one of Colombia's most prominent families in a nation where the sons of the wealthy usually avoid military service.

For decades, the Santos family published the Bogota daily El Tiempo, the country's most important newspaper. Juan Manuel's great uncle, Eduardo Santos, was president from 1938-42.

Though he worked at El Tiempo as an editor, Juan Manuel Santos is said to have been grooming himself for the presidency since he was a teenager. At one point, he reportedly shaved off his beard because he thought he would look more presidential.

He served in several governments but came to national prominence in 2006 as defence minister. He teamed up with President Alvaro Uribe to wage a U.S.-backed military offensive against the FARC that cut the rebel forces in half to about 7,000 fighters.

Pledging to continue these hardline policies, Santos won the presidency by a landslide in 2010.

Tense negotiations

FARC guerrilla fighters patrol through long grass in the jungle near the town of Miraflores, 300 kilometres southeast of the capital Bogota, on Aug. 7, 1998. (Henry Romero/Reuters) But soon after, he sent his brother and other envoys to Havana to open secret talks with the FARC. He calculated the guerrillas had been weakened to the point they would finally be ready to cut a deal and pursue their goals through politics.

Four years of tense negotiations finally culminated in a peace agreement signed last month in Cartagena before 2,500 diplomats and invited guests, including UN Secretary General Ban Ki-moon.

There was talk of making the date, Sept. 26, a national holiday.

Quoting Colombia's national anthem, Santos declared: "The horrible night is finally over."

Only it wasn't.

Many Colombians viewed Santos as a traitor for reaching out to the FARC, a guerrilla army that funded its war with profits from drug trafficking, extortion and other crimes. The FARC also committed massive human rights abuses, like massacres and the kidnapping of thousands of civilians for ransom.

Critics say deal too lenient

Critics, led by his former boss Uribe, complained the peace agreement was too lenient on the FARC because it would allow rebels accused of war crimes to avoid prison if they confess before a special tribunal.

Amid flooding caused by Hurricane Matthew, only 37% of the electorate turned out. Despite polls showing the agreement would easily pass, the "no" vote topped the "yes" vote by less than one half of one percentage point.

Uribe and his allies are now demanding the accords be renegotiated. They want FARC leaders to serve lengthy prison terms and to be banned from holding elected office. They also object to provisions that would give a future FARC-led political party 10 guaranteed seats in Congress between 2018 and 2026.

On Friday, Uribe tweeted his congratulations to Santos, but added tersely: "I hope this leads to changes in these accords that are damaging to democracy."

'No' supporters celebrate following their victory in the referendum last Sunday. Critics of the proposed deal say it's too lenient on rebels accused of war crimes. (Mario Tama/Getty Images) But it's unclear whether the FARC would be willing to backtrack on concessions that required years to extract.

Meanwhile, rebel foot soldiers who were preparing to gather in special zones around the country and turn over their weapons to UN inspectors are now in limbo.

A ceasefire declared until Oct. 31 is still holding and could be renewed. But FARC leaders, while stating emphatically that they want peace, have cautioned their rebels to protect themselves and be prepared for war. On Thursday, army officers instructed their troops "to be on maximum readiness for combat."

In its citation, the Nobel committee warned: "There is a real danger that the peace process will come to a halt and that civil war will flare up again. This makes it even more important that the parties ... continue to respect the ceasefire."​