Colombian soldiers patrol along a dirt road in Miranda, Colombia, on January 18, 2012.

Story highlights

NEW: A mediator says the rebel group will begin releasing 10 hostages Monday

One operation occurs in an area where 11 troops were killed over the weekend

The defense member calls the operation "one of the greatest blows" against the rebels

A top leader of one faction of the Revolutionary Armed Forces of Colombia is captured, he says

Bogota, Colombia CNN  — 

Colombian authorities have killed dozens of leftist guerrillas in the past day, the nation’s defense minister said Wednesday.

Operations throughout the country led to the killing of 39 suspected members the Revolutionary Armed Forces of Colombia and the capture of a dozen others from the rebel group, Defense Minister Juan Carlos Pinzon told reporters.

“This is one of the greatest blows (to the rebel group) in the last five years,” Pinzon said.

One operation near the Venezuelan border led to the killing of 36 suspected rebels and the capture of five others, including a top leader of one faction of the rebel group, he said.

The joint military-police operation occurred in the department of Arauca, where over the weekend authorities said rebels killed 11 troops in an attack.

The Revolutionary Armed Forces of Colombia, known as the FARC, has been at war with the Colombian government since the 1960s. While severely weakened in recent years, the guerrilla group has continued to carry out kidnappings and attack security forces.

A mediator said Wednesday that the FARC will begin releasing its 10 remaining government hostages on Monday.

“With much joy and satisfaction we want to inform you that next Monday the FARC will hand over the 10 uniformed people, police and soldiers, that are in their control,” said Piedad Cordoba, a former senator who has helped coordinate hostage handovers in the past.

The hostage release could take two days, Cordoba said. She did not specify where it would take place.

In December, the FARC announced the planned release of six national police officers in the group, but later postponed their release because of an alleged militarization in the area where the rebels operate.

Journalist Fernando Ramos contributed to this report.