CARACAS, Venezuela -- Colombia and the nation’s largest guerrilla group will begin formal peace talks the first half of October, as the two sides say they are determined to put an end to a half-century conflict that has killed tens of thousands and once made this Andean nation a regional pariah.

On Tuesday, President Juan Manuel Santos said that after six months of informal and largely secret talks in Cuba, government officials and the Revolutionary Armed Forces of Colombia, or FARC, had hammered out a roadmap that could lead to peace.

“I have the conviction that we are facing the real opportunity of finishing our armed internal conflict once and for all,” Santos said. “It’s a difficult path, very difficult, but it’s a path we have to explore.”

Amid months of rumors that talks were in the works, Santos admitted last week that the two sides were on the verge of negotiations.

In a video response to Santos, the FARC’s top commander Rodrigo Londoño Echeverry, known as Timochenko, said both sides had hammered out the “General Agreement to End the Conflict” on August 27.

“The way out is not war but civilized dialogue,” Timochenko said in the video, which was broadcast in Cuba and posted on YouTube.

The bearded commander also lamented the breakdown of peace talks 10 years ago and the ensuing military confrontation.

“Colombia in its entirety needs to stand up and make sure that doesn’t happen again,” he said. “Our country doesn’t deserve this war that was declared against it.”

One of Santos’ largest challenges is overcoming the specter of those failed talks. Initiated under the Andrés Pastrana administration in 1998, Colombia eventually demilitarized an area the size of Switzerland as a concession to the FARC. When the talks broke down in 2002, many blamed the detente for allowing the FARC to build their strength and wreak havoc for the next decade.

On Tuesday, Santos reassured the nation that he’d learned from the past. This time there will be no territorial concessions and the government will keep up the military pressure on the guerrilla group even as it pursues talks, he said.

“I repeat, the government will not make any military concessions,” Santos said. But he also asked Colombians to be patient amid new attacks by the FARC.

Analysts have said that increased violence is likely, as both sides flex their muscle as they jockey for position at the negotiating table.

The talks will cover five main areas: the end of the armed conflict, drug trafficking, rural development, opposition political rights, and victims’ rights.

Santos said the talks would be on strict timeline and “would be measured in months, not years.”

If there was not enough progress, he said, they would be broken off.

Santos said Norway and Cuba had been key to bringing the peace talks about, along with Venezuela. Venezuela and Chile will be observers of the process.

On Tuesday, Venezuelan President Hugo Chávez hailed the news and called on Latin America to “accompany our brother Colombia in its efforts to achieve peace.”

The FARC was founded in 1964 with Marxist underpinnings, but it has increasingly resorted to drug trafficking and extortion to finance its survival. Although it’s only thought to have about 9,000 active members, the group has proved successful at staging damaging and demoralizing hit and run attacks.

The talks will likely have deep political implications for Santos as he looks toward potential reelection in 2014. His adversaries, including the popular former president Alvaro Uribe, have accused him of selling out the nation to negotiate with the FARC.

“Without a doubt there are risks, but I think history will be much more severe with all of us if we do not take advantage of this opportunity,” Santos said Tuesday. “In any case, the responsibility for this decision falls on no ones shoulders but mine.”