The stunning victory of the "no" camp in Sunday's referendum has put Colombia's historic peace deal with leftist rebels in jeopardy. The vote, which opponents of the pact won by a razor-thin margin, flew in the face of expectations and upended years of diplomatic efforts and negotiations with the leftist FARC rebels, who have waged one of the world's longest insurgencies.

“Now we have to decide what path to take so that peace will be possible," said President Jose Manuel Santos, who has staked his political legitimacy on the peace process. "I won’t give up.”

As he and his counterparts from the FARC, known formally as the Revolutionary Armed Forces of Colombia, struggle to chart a way forward in a moment of profound uncertainty, the vote has made another unwelcome development more certain. It is likely to have scuppered the chance for Santos and the FARC leadership to win this year's Nobel Peace Prize, which will be announced Friday.

"Colombia's off any credible list," Kristian Berg Harpviken, head of the Peace Research Institute in Oslo and a prominent speculator on possible contenders for the prestigious annual award, told reporters on Monday.

The Nobel committee frequently rewards the architects of peace processes, including in Northern Ireland in 1998, the Oslo Accords between the Israelis and the Palestinians in 1994, and veteran Finnish diplomat Martti Ahtisaari, who won the award in 2008 for a career in peacemaking.

Colombia's war with the FARC has lasted decades and killed more than 220,000 people. The landmark resolution to the conflict, and an agreed road map to bring the rebels out of the jungle, was considered so historic that both Santos and FARC leader Rodrigo Londoño, known by his nom de guerre Timochenko, were front-runners to win the prize.

"It's now out of the question," Asle Sveen, a historian who has written several books on the Nobel Prize, told Reuters. According to the news agency, he had earlier tipped the Colombian government to win.

Other candidates for the prize this year include the lead Western negotiators of the nuclear deal with Iran, former National Security Agency whistleblower Edward Snowden, Pope Francis and a Russian human rights advocate.

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