Colombia's military denied a claim by the FARC rebel group that eight soldiers were killed this week in a counter-insurgency operation.

Military sources disclosed, however, that a soldier was killed in a separate engagement on January 9 in the southern department of Caqueta.

The soldier, 23-year-old Edward Valsco Medina, was believed to be the first combat death since the Revolutionary Armed Forces of Colombia (FARC) unilaterally declared a ceasefire on December 20.

The Bogota government and the FARC have been in peace talks for more than two years, aimed at putting an end to the oldest leftist insurgency in Latin America.

"It's not true that 8 of our soldiers have been assassinated by #Farc in #Meta," the army tweeted.

The rebel group said eight soldiers were killed in central Meta province earlier this week after one of its units came under mortar and air attack.

"As a result of the defensive response, we lament that eight military personnel lost their lives, unnecessarily," it said in a statement from Havana, where peace talks are underway.

The rebels said a Colombian soldier also was wounded during a separate counter-insurgency operation in the northern Antioquia and Uraba regions.

"These are all casualties that could have been avoided if the government had been less small-minded," it said.

The FARC urged the government to stop "these senseless actions in the midst of a peace process, because they could provoke the end of the unilateral ceasefire and disturb the climate of confidence that should prevail at the negotiating table."

The rebel group unilaterally declared an indefinite ceasefire on December 20, a stance it reaffirmed on Tuesday.

President Juan Manuel Santos has refused to commit to a truce until the FARC signs onto a comprehensive peace agreement.

Peace talks have been taking place in Havana for more than two years, and remain a high priority for Santos, who has made ending the 50-year-old insurgency the central goal of his presidency.

More than 220,000 people have lost their lives in the conflict.

The peace talks have been in recess since December, but they are scheduled to resume January 18 with an experts-level meeting, followed by the start of the next cycle of negotiations on January 26.