HAVANA, Cuba -- The top negotiator for Colombia's main rebel group announced a unilateral cease-fire on Monday, before heading into much-anticipated peace talks with government counterparts in the Cuban capital of Havana.

Ivan Marquez said the Revolutionary Armed Forces of Colombia would stop all military operations and acts of sabotage against government and private property starting at midnight Monday and running through Jan. 20.

Marquez said the move was "aimed at strengthening the climate of understanding necessary for the parties to start a dialogue."

There was no immediate response to the rebel overture from the government of Colombian President Juan Manuel Santos, and government negotiators in Havana also refused to comment before heading into the talks.

But analysts said the move puts pressure on Colombia to reciprocate in some way. Santos has so far refused to consider a cease-fire during the talks.

"What they just announced puts the rebels in the vanguard and is very, very important," said Piedad Cordoba, a former Colombian senator who has led past peace efforts and negotiated the release of several hostages held by the rebels. "The Christmas cease-fire wins (the rebels) credibility and legitimacy."

"It certainly puts political pressure on the Santos government" not to attack the rebels during the talks, said Adam Isacson, an analyst at the Washington Office on Latin America.

The talks got underway under threatening skies at a convention centre in Havana, with most rebel and government negotiators dressed casually in short-sleeve shirts or guayaberas.

The rebel delegation came sporting a life-size cardboard cutout of Simon Trinidad, a FARC leader named to the negotiating committee despite the fact he is serving a 60-year jail term in the United States and is unable to attend.

Among the rebels at the talks was Tanja Nijmeijer, a 34-year-old Dutch woman who once studied Romance languages in her native country before joining the rebels more than a decade ago. Nijmeijer, was the only woman at the negotiating table, entered the convention centre wearing a dark beret with a FARC insignia.

Cuba is playing host to the talks in Havana following an initial round of discussions in Oslo, Norway last month. The FARC has been at war with the Colombian government for nearly half a century. There is no deadline for agreement, though both sides say success must come within months, not years.

The talks, the result of seven months of secret negotiations in Havana, follow several failed efforts over the decades to end the conflict. Land reform, the heart of the conflict, is at the top of the agenda.

The government is hoping peace leads to greater foreign investment in mining industries. It has promised to return millions of acres of stolen land to displaced peasants, one of the rebels' main demands.

The 9,000-strong FARC is being asked as a condition of peace to help end the cocaine trade that has funded its struggle. Colombians also want it to account for the dozens of kidnap victims who have disappeared in its custody and other noncombatants it is accused of killing.