The discussions, which had been set to begin on Thursday, are the latest attempt to resolve a five-decade war that has left thousands dead and millions more displaced since the founding of the Revolutionary Armed Forces of Colombia, or FARC.

Negotiations promise to be complicated, with items on the agenda that will almost certainly cause roadblocks and heated discussion. The five-point agenda kicks off with an analysis of rural development.

"Delegates of the national government and the FARC agreed to continue technical meetings to finalize details of mechanisms for citizen participation," said a statement sent by the president's office on Tuesday.

"On Monday the 19th in Havana, Cuba, the negotiators will start discussion on the agreed agenda."

The statement did not elaborate on what it meant by citizen participation, but civil groups have called for the inclusion of other parties in addition to the two warring sides and mediators.

Past negotiations have been bogged down by the involvement of a range of actors pushing different agendas and played out before the world's media in a tent in Colombia's jungles.

While talks this time will be secret and the FARC comes to the table weakened, the rebels are by no means a spent force.

A decade of U.S.-backed blows against the drug-funded group has battered it to the point that President Juan Manuel Santos believes it will seriously seek to end the fighting.

Its ranks have been cut in half and several of its toughest and most dedicated leaders have been killed or captured.

But in an effort to demonstrate that it is still relevant, the group has stepped up attacks on economic and military targets this year.

Santos, who was traveling to Portugal, said that the success of the talks depended on the FARC.

"We hope that good will is demonstrated at the negotiating table," Santos said as he arrived in Lisbon for a state visit.

"If there is good will there will be agreements, and if there is no good will, well, there'll be no accord."

Santos, who may run for re-election in 2014, says the government wants to reach a deal in a matter of months, not years, while the FARC says it will sit at the table as long as necessary.

"It is clear that both sides have a long way to go in order to seek common ground," Heather Berkman, an analyst with Eurasia Group, wrote in a note to clients this week.

"We see current negotiations as broadly moving in the right direction and still expect the government and FARC to hash out an agreement in 2013."

(Reporting by Helen Murphy, Editing by Jackie Frank and Cynthia Osterman)