MEXICO CITY — The gruesome discovery of 32 bodies scattered in houses in the port city of Veracruz this week is the latest sign that Mexico's drug-fueled violence is entering a new phase in which murky paramilitary-style squads are carrying out mass exterminations.

A spokesman for Mexico's marines, Jose Luis Vergara, said Friday that troops had arrested eight suspected members of a squad known as "Zeta Killers" on Thursday and that their confessions led troops to three houses where they discovered the bodies.

It was the latest ghastly event to send shudders through Veracruz. Two weeks ago, gunmen dumped 35 semi-nude, mutilated bodies along a freeway underpass in Veracruz in broad daylight.

Authorities said at least some of the victims in both instances were members of Los Zetas, a violent crime group whose reach now stretches beyond Mexico's borders.

The spate of summary killings underscores the shifting panorama of Mexico's violence, which is surging in the states of Veracruz, on the Gulf of Mexico, and Guerrero, on the Pacific.

Opponents of President Felipe Calderon, whose policies have been widely criticized for failing to curb, or perhaps even feeding, the violence, say the recent killings indicate the emergence of paramilitary vengeance squads.

At a news conference, Vergara narrated as marines paraded the eight men before reporters, identifying a middle-aged man with a neatly trimmed beard, Alfredo "El Capi" Carmona Aranda, as the group's ringleader in Veracruz state.

Using information obtained from the arrests, Vergara said marines went to a house in the Jardines de Mocambo district of Veracruz, where they found 20 bodies. At another house in the Costa Verde district, they found 11 more bodies. The last body was discovered in a house in the Costa de Oro district, he said.

The Zeta Killers group, which also calls itself New Generation, first came to light in a YouTube video in late July. Masked men carrying automatic weapons vowed to cleanse Veracruz state of criminals belonging to Los Zetas, a brutal group given to beheading and disemboweling rivals and imposing stiff extortion fees in areas of their control.

Veracruz, the nation's largest and oldest port, is a key transit point for narcotics, chemicals used to make synthetic drugs and the movement of migrants toward the U.S. border.

Long a bastion of Los Zetas, it has become a battleground with rivals who work under the umbrella of the Sinaloa crime group, experts say.

The dumping of the 35 bodies along a Veracruz highway during the afternoon rush hour Sept. 20 led Calderon last week to deploy 2,000 marines and additional federal police in the state. Aides later said the federal forces would put 21,035 state and municipal police in Veracruz under scrutiny and purge those linked to crime groups.

Still, the manner in which four vehicles maneuvered along the highway, blocked traffic and dumped the bodies led some experts to see a unique style to the recent killing spree.

"These were people who had military training," said Alberto Islas, a security analyst and chief of Risk Evaluation Ltd.

Islas said the military-style movements of various crime groups indicate that "President Calderon doesn't have control of the armed forces."

In a separate commentary reflecting a growing view within the political left, Raymundo Riva Palacios wrote Friday in an Internet essay that members of the Calderon government risk being hauled before international tribunals after they leave office in late 2012 "on charges linked to this dirty war which they don't acknowledge but that the evidence increasingly shows exists."