EL DIAMANTE, Colombia (CNN) -- Fighting between leftist rebels and a right-wing paramilitary group in northern Colombia has killed more than 30 people, some reportedly beheaded.

At least three children were among the victims, including a baby less than a month old.

Rebels of the Revolutionary Armed Forces of Colombia (FARC) began an offensive early in the week with an attack on El Diamante, a village in Cordoba state, about 460 kilometers (285 miles) northwest of Bogota.

The village is a stronghold of FARC's archenemy, Carlos Castano, the leader of the United Self-Defense Forces of Colombia (AUC), an alliance of rightist paramilitary groups that have battled FARC for the past decade.

FARC claimed that Castano was killed in the attack, but AUC said he survived and was leading a counteroffensive.

Colombian television broadcast gruesome images of severed heads lying yards away from the bloodied corpses. The fighting, the fiercest in many weeks, seemed sure to sicken public opinion just days before peace talks between FARC and the government.

"The villages are totally destroyed. There's only desolation and death. This was ... the vile massacre and genocide of civilians," said Gen. Victor Alvarez, a regional army commander.

"We found bodies without heads. It was terrifying. Nearby, there's a paramilitary camp, and it seems the (FARC) rebels attacked the camp first and then turned on the civilians and burned all the houses in the village," said the parish priest, Rev. Joaquin Pachon, in a interview with the Radionet radio network.

Health officials in the nearby town of Tierralta said the dead included a 3-week-old baby hit in the head with a stray bullet, a 7-year-old girl stabbed in the stomach with a machete and an elderly woman.

"One would rather not believe that men are capable of this. It was pure barbarity," said Dr. Viviano Guerrero of the Tierralta Health Department.

Government peace commissioner Victor Ricardo said he did not believe the fighting would change the start of the peace talks, set to begin January 7 in southern Caqueta province.

Reuters contributed to this report.