(TIME Magazine) It was supposed to be a feel-good photo op. At a ceremony on Thursday in Oslo, the Colombian government and Marxist insurgents formally launched peace talks to end Latin America’s last remaining guerrilla war — which, after 48 years, is also one of the region’s longest and bloodiest ever. But the lead negotiator for the Revolutionary Armed Forces of Colombia, or FARC, refused to play along.

FARC’s Iván Márquez attends a peace-talk ceremony at the Hurdalsjoen Hotel in Hurdal, near Oslo, on Oct. 18, 2012

Iván Márquez, a veteran FARC comandante, took the microphone and launched into a 35-minute rant against the Colombian upper class, sell-out government officials, foreign oil and mining companies and capitalism in general. He made no apologies for his organization’s battlefield abuses and went on to suggest that peace would not be achieved through “the silencing of guns” but by adhering to the FARC’s communist vision.

The Márquez manifesto shocked Colombians who had expected a tad more modesty from the FARC, which has seen its numbers cut by more than half, to about 8,000 fighters, after a decadelong army offensive. The tirade immediately shifted the national mood from one of cautious optimism to concern that this fourth attempt at peace talks with the guerrillas since the 1980s might fail like the past three. “Could it be,” said Antonio Navarro Wolff, a Colombian politician and former guerrilla, “that history will repeat itself?”

Others warned against reading too much into Márquez’s incendiary rhetoric, which was likely designed to boost the morale of guerrillas still fighting in the jungle by assuring them that their leaders would not back down. But even so, if such tone-deaf belligerence continues it could erode vital public support in Colombia for the peace process. “It was the worst imaginable way” for the peace talks to begin, wrote Kevin Howlett, a British political analyst, in a column for the Colombia Reports news website. “Their views have a right to be heard. But the FARC has absolutely no right to pretend that they can impose their vision at the negotiating table. Colombia will not accept it.”

Humberto de la Calle, lead negotiator for Colombian President Juan Manuel Santos, quickly assured the country that its political and economic model is not up for debate in the negotiations that begin on Nov. 15 in Havana. If the FARC thinks it has the answers, he said, its fighters should disarm and then test their ideas by running for political office, as have many former Latin American guerrillas, including the Presidents of Brazil and Uruguay and Bogotá Mayor Gustavo Petro. Indeed, the mechanism for the demobilization of FARC fighters and their participation in politics will be key issues in Havana.

But two other issues on the agenda — the development of Colombia’s woefully neglected rural provinces and reparations for war victims — could turn out to be especially controversial. In those areas, Márquez painted the FARC as the principal injured party in the war, especially since thousands of FARC supporters have been slaughtered by paramilitary armies that often worked in collaboration with the army before they were disbanded in the 2000s. Those right-wing militias also killed off some 3,000 members of the Patriotic Union, a prorebel political party founded in the 1980s, which is one reason why the guerrillas have long resisted turning in their weapons.

Yet at the same time, Márquez stubbornly refused to acknowledge the myriad war crimes committed by his own fighters — most infamously the thousands of Colombians the FARC has kidnapped over the years. Many were freed in exchange for ransom payments, which along with drug trafficking is a main FARC revenue source. But the FARC has refused to account for about 500 of its hostages, and they are widely thought to be dead. “The guerrillas present themselves as the biggest victims but make no mention of the victims of their own violence,” says Clara Rojas, director of the Free Country Foundation, which counsels the families of hostages. In Oslo, de la Calle insisted the FARC make a full accounting for their hostages as part of the peace process. Meanwhile, 32 relatives of hostages unaccounted for announced they’ll travel to Havana to press the FARC for more information.

Then there’s land reform, which has been a key FARC demand since the rebels first took up arms in 1964. At the negotiating table, the FARC is sure to bring up the fact that just 1.15% of Colombia’s population owns 52% of the nation’s total land, an astonishing disparity that has helped make Colombia the world’s seventh most unequal country, according to the World Bank. But the FARC itself is guilty of unjust land grabs. The fighting has driven thousands of peasant farmers off their plots and into urban slums, and many of their properties have been occupied by the guerrillas. According to Colombian Senator Juan Fernando Cristo, 30% of the claims lodged by displaced farmers under the government’s new land-restitution law blame FARC commanders for stealing their land — a total of more than 700,000 hectares.

It may be that sitting across from government negotiators behind closed doors, Márquez’s bluster will give way to more sober, reality-based positions. Either way, his Oslo outburst reinforced the Colombian government’s concern that leaks and off-the-cuff remarks to the media could do real damage to the peace process. As a result, there will only be occasional public progress reports during the negotiations, which are expected to last for at least a year. In the words of de la Calle: “We are not going to conduct peace talks through a microphone.”