Colombia's FARC rebels say ceasefire to end January 20

Colombia's FARC rebel group member Andres Paris (R) receives from National University of Colombia professor Marco Romero, proposals on agricultural reforms obtained from a farmers' forum in Colombia, in Havana January 9, 2013.

HAVANA (Reuters) - A unilateral ceasefire declared at the beginning of peace talks with the Colombian government in November will end on January 20 unless the government agrees to also lay down its arms, the country's Marxist FARC rebels said on Wednesday.

The rebels announced the ceasefire on November 19, the first day of peace talks in Havana aimed at ending five decades of conflict in Colombia, but said it would last only two months if the government did not observe the truce.

Colombian President Juan Manuel Santos has refused to take part, choosing instead to keep up military pressure to try to force the FARC, or Revolutionary Armed Forces of Colombia, to reach an accord.

"There will not be an extension of a unilateral ceasefire," FARC lead negotiator Ivan Marquez told a news conference in the Cuban capital.

"Only the signing of a bilateral ceasefire would be possible, if the government deems such a measure reasonable," he said.

The FARC and Colombia's government are in the early stages of the latest effort to end a war that dates back to the guerilla group's formation as a communist agrarian movement in 1964.

Thousands of people have died and millions have been displaced in what has become Latin America's longest running rebel insurgency.

During the ceasefire, government attacks have killed at least 34 rebels.

At the same time, the Colombian military and police have accused the FARC of attacking troops and infrastructure.

The rebels are believed to be weakened after years of a U.S.-backed offensive by Colombian forces.

The peace talks, which are attempting to address the basic causes of the conflict such as rural poverty, concentration of land ownership and social inequality, broke before Christmas and are not scheduled to resume until Monday.

They are being held at a convention center in Havana, mostly out of the public eye.

(Editing by Jeff Franks and Christopher Wilson)