A top FARC negotiator Tuesday reaffirmed the Colombian rebel group's intention to observe a unilateral ceasefire so long as its forces do not come under attack.

In comments published in the newspaper El Espectator, Pastor Alape said the indefinite ceasefire that the FARC declared on December 20 was "a serious step toward the agreement of an armistice."

"The unilateral and indefinite ceasefire will remain in place as long as the military does not attack the FARC's units," said Alape, whose real name is Felix Antonio Munoz.

The FARC charged in a statement at the end of last week that the military was stepping up its pressure on the guerrilla units.

Colombia's President Juan Manuel Santos has acknowledged that the FARC has abided by the ceasefire.

But he has refused to agree to a ceasefire on the part of the government until a comprehensive peace agreement has been reached.

The government and the FARC have been negotiating for more than two years in Havana to bring an end to the group's 50-year-old insurgency, but key issues remain unresolved, including disarmament and how any agreement should be ratified.

More than 220,000 people have died in the conflict, Latin America's longest.