Mexico's army announced Friday that it had detained a fourth high-ranking officer during a civilian investigation into alleged military links to drug cartels. Three generals were previously detained.

The Defense Department said it brought in retired Lt. Col. Silvio Hernandez Soto for questioning, noting he was named in the same round of detention orders issued May 7 that included the other officers. However, the department did not specify what the allegations against him were. None of the officers has yet been charged.

Retired Gen. Tomas Angeles Dauahare and Gen. Roberto Dawe Gonzalez were detained on Tuesday and are being held at least 40 days while prosecutors strengthen their case. Retired Gen. Ricardo Escorcia was brought in for questioning on Thursday.

While a higher-ranking army official, three-star-Gen. Jesus Gutierrez Rebollo, then head of Mexico's anti-drug agency, was arrested in 1997 and later convicted of aiding deceased drug lord Amado Carrillo Fuentes, the detentions this week represented the largest single group of high-ranking Mexican army officers detained in recent memory.

An official at the Attorney General's Office said earlier that Angeles Dauahare and Dawe Gonzalez are suspected of protecting members of the Beltran Leyva cartel. He spoke on condition of anonymity because he is not allowed to discuss the case.

The investigation against them is based on a case from 2009, the Attorney General's Office said.

President Felipe Calderon named Angeles Dauahare as assistant defense secretary in 2006. He left the post in 2008, when he retired.

Dawe Gonzalez is currently assigned to a military base in the western state of Colima.

Escorcia retired from active service in 2010 after reaching mandatory retirement age, but previously served as head of the military base in Cuernavaca, a city just south of the Mexican capital that has been considered Beltran Leyva territory.

The leader of the cartel, Arturo Beltran Leyva, was killed in a shootout with Mexican marines at an apartment complex in Cuernavaca in 2009. The marines were reportedly called in to look for the capo after the army appeared to be slow to act on U.S. intelligence indicating the drug lord's location, according to a leaked U.S. Embassy diplomatic cable from late 2009.

Angeles Dauahare's lawyer, Alejandro Ortega, said on Thursday that he hasn't been allowed to talk to his client, but he said the general told his wife he is being accused of taking money from associates of Edgar Valdez Villareal, who was allegedly top hit man for Beltran Leyva. Valdez Villareal was arrested in 2010.

Ortega said the general supports himself with an army pension and owns a house and an apartment. He said the general's wife also owns a house she inherited.

A few senior military officers have been arrested for alleged links to traffickers during Mexico's long struggle to control the cartels.

Retired Gen. Juan Manuel Barragan Espinosa was detained in February for alleged links to organized crime and Gen. Manuel Moreno Avina and 29 soldiers who were under his command in the border town of Ojinaga, across the border from Presidio, Texas, are being tried on charges of torture, homicide, drug trafficking and other crimes.

More than 47,000 people have been killed in drug violence since Calderon deployed thousands of soldiers to drug hotspots, according to government figures.

Also Friday, the army said it had detained eight suspected members of the Gulf cartel and seized drugs, guns and hand grenades during investigations into the May 13 discovery of 49 dismembered bodies on a highway in northern Mexico.

The Defense Department said the suspects were caught Thursday as part of an operation designed to capture those responsible for the grisly discovery in the city of Cadereyta. But the department did not say whether the eight suspects were directly involved in those killings.

Authorities had previously suggested the rival Zetas cartel was responsible for the killings.