By JUAN FORERO
 
BOGOTÁ, Colombia, June 16 - The massacre of 34 coca farmers in northeastern Colombia on Tuesday by leftist rebels may be a sign that the guerrillas are intent on regaining territory they have lost to a right-wing paramilitary group, political analysts said Wednesday.

The paramilitaries have been engaged in informal disarmament talks with the government of President Álvaro Uribe in the last year, and had recently pulled back some of their forces from the area where the violence occurred, the analysts said.

Fighters from the Revolutionary Armed Forces of Colombia, a Marxist insurgency known as FARC, entered San Martín, a hamlet in the Norte de Santander province, on Tuesday morning, tied up coca farmers employed by the paramilitaries and shot them dead, said survivors, army commanders and local government officials. It was the worst mass killing in Colombia since Mr. Uribe won office two years ago.

The farmers raised coca, the prime ingredient in cocaine, for paramilitary groups that have been battling the rebels across Colombia for control of vast fields of coca.

The attack came on the same day representatives of Mr. Uribe's government met with paramilitary leaders and announced that formal talks with the group would begin July 1. But political analysts said Mr. Uribe's negotiations with the paramilitaries could lead to increased violence as the FARC tries to recover territory lost to paramilitary groups.

"You can do all the negotiating you want with the paramilitaries, but as long as the guerrillas and narco-trafficking are there, you're going to have violence like this," said Daniel García-Peña, a former government disarmament negotiator who now runs a left-leaning peace group.

Alfredo Rangel, a security analyst and former adviser to the Defense Ministry, said the massacre could mark a new stage in which the rebels embark on a brutal counteroffensive. "This massacre announced that the withdrawal of paramilitaries from some zones will lead to intense efforts by the guerrillas to bring those zones under their control," he said.

The paramilitaries, though long tied to the drug trade, began disarmament talks with the government after American officials indicted three top leaders on drug trafficking charges and sought their extradition in 2002.

But while the paramilitaries talk peace, human rights groups and foreign diplomats say, they have not completely abandoned the most important drug-producing regions, like the isolated swath of jungle near the Venezuelan border where Tuesday's attack took place.

"There is no cease-fire on the part of the paramilitaries," said Diana Sánchez, who investigates abuses for Minga, a local rights group in Bogotá. In April a paramilitary group killed 12 Wayuu Indians in Guajira province, and in May another team of paramilitaries killed 11 peasants in Arauca province. Still, there has been a drop in recent months of such mass killings.

But the guerrillas have increasingly carried out mass killings aimed at terrorizing villagers who have supported the paramilitaries.

"The paramilitaries used massacre with intensity in their fight for territory the guerrillas controlled," said Mr. Rangel. "Now there's an inverse of that in some areas. It's the guerrillas who come in where the paramilitaries are and use this instrument, the massacre, as a way to recover the territory."
 

Monica Trujillo contributed reporting from Bogotá for this article.