Colombia's government and leftist FARC rebels resume peace talks in Cuba on Monday after a three-week break, under pressure to show results in the coming months to finally end their half-century-old conflict.

The longtime rivals launched the negotiations in October, their fourth attempt in three decades to close a battle that has left 600,000 people dead, 15,000 missing and four million displaced since 1964.

After taking a holiday break on December 22, the two sides face a crucial year as President Juan Manuel Santos has warned that the negotiations must conclude by November.

Though the guerrilla group has declared a unilateral ceasefire until January 20, the government has continued its offensive against the rebels, accusing them of failing to respect their own truce by planting landmines and attacking civilians and soldiers.

"The Colombian public forces will continue to tirelessly pursue criminals, as the constitution and all the Colombian people demand," Defense Minister Juan Carlos Pinzon said Friday. "It does not matter whether they are FARC terrorists" or criminal gangs, he said.

The Marxist rebels said Wednesday that they would not extend their ceasefire unless the government declares one too.

The Revolutionary Armed Forces of Colombia (FARC) took up arms in 1964 to protest against the concentration of land ownership in the country, but a string of military defeats has cut its ranks to 9,000 -- half of what it was in the late 1990s.

The key issue in the dispute, rural development, will be on the agenda when talks resume on Monday.

The government representatives, headed by former vice president Humberto de la Calle, are expected to travel to Havana on Sunday. The guerrilla delegation is already in the communist island's capital.

"There is hope that the negotiation continues to move forward in good terms. I think we could see some results in the middle of the year," Ariel Avila, an analyst at the CNAI think tank, which studies the Colombian conflict.

"The challenge will be ... the acceptance of any agreement by part of the population," he said.

Christian Voelkel, an expert on Colombia at the independent International Crisis Group, said it was difficult to predict when the first preliminary agreements will be announced since the talks are behind closed doors.

"But, without a doubt, pressure will increase in 2013 for the negotiation to show results due to the deadline given by President Juan Manuel Santos and the country's expectations," Voelkel said.

In addition to land reform, the negotiations will include drug trafficking, political participation, disarmament and victims' rights.

The guerrilla group and the government will have to work hard for Colombian society to accept the agreements they might reach, Voelkel said.

"There is good will in the country, but also a lot of unknowns," he said.

There is also international support, with Norway hosting the launch of the talks in October while Cuba has hosted the negotiations since November with Venezuela and Chile accompanying the process.

Venezuelan President Hugo Chavez was considered a key facilitator in the process, but the ailing leftist leader has been out of public sight since undergoing a fourth round of cancer surgery in Havana on December 11.

"President Chavez, from his sickbed, has had the courtesy of intervening during some difficult moments, contributing with his enormous prestige to smooth things over," a rebel commander, Mauricio Jaramillo, said this week.

Santos said his Venezuelan counterpart has been a "key person" in the talks, and "for this reason I wish him well, because we really need him."

Political analyst Fernando Giraldo said Chavez is trusted by both Santos and the FARC and his absence creates a less favorable environment.

"Chavez's opinion counts a lot for the FARC leadership and it is unclear whether another leader would have the same influence," Giraldo said.

But CNAI's Avila said the fate of the negotiations are not tied to Chavez or Venezuela.

"His absence will affect the mood a little bit, but it won't be decisive," he said. "Venezuela has already participated and helped. Chavez has already been there for the first part of the process, which was very important."