The Revolutionary Armed Forces of Colombia, or FARC, doubts that a peace agreement with the Colombian government will be finalized just in time for the March 23 deadline despite President Juan Manuel Santos' call for a faster process.

Both sides have been negotiating in Cuba for three years now to effectively put a stop to their 50 years of armed conflict, which has killed 220,000 and displaced millions of people, Reuters reported.

The government and the FARC have arrived at a breakthrough on Sept. 23, when the two parties set a six-month deadline for a final agreement, the news outlet noted. For this announcement, Santos traveled to Havana and shook hands with guerilla leader Timochenko and Cuba's President Raúl Castro.

"We are trying to do the impossible to make the 23rd (of March), but there are objective reasons that certainly will prevent us from reaching it," Joaquin Gomez, one of the FARC negotiators, told reporters in Havana, as quoted in Reuters' report. "There are major stumbling blocks such as the clarification and dismantling of paramilitary groups, plus a large number of others, that have not been possible to overcome, and not because we are intentionally against the deadline."

Santos and the government's chief negotiator, Humberto de la Calle, have both said that the two sides aim to work long hours and will not end negotiations until the deadline for a final deal is accomplished, teleSUR reported. The negotiations have been divided into smaller sessions, with short breaks given between them.

The Colombian president also announced that he intends to call special sessions of Congress to clear any difficulties in the process, Reuters added.

Several tough issues still need to be addressed such as the disarmament, demobilization, and concentration of the guerrillas, a bilateral cease-fire, and whether or not the final agreement will arrive at a public referendum, according to teleSUR.

Colombian voters will then have a chance to approve any comprehensive agreement in the final agenda, Reuters noted.

The two sides are unable to meet eye-to-eye when it comes to the details. The Colombian government wants the disarmament of combatants, while the FARC is pushing for the "laying down of arms," a somewhat different language that implies that they do not mean to give up their weapons, teleSUR further reported.

FARC's resolve came out of the failure of past peace talks where thousands of demobilized guerilla members were murdered and plenty were forced to go back to armed struggle, teleSUR added. The group's concerns also include the demobilization of paramilitary groups or death squads, the FARC's involvement in national politics, and the release of their members from prison.