Gunmen killed a state congressional candidate and his wife and two sons in their home Saturday in the Gulf coast state of Tabasco, in southern Mexico.
Jose Francisco Fuentes Esperon, 43, was found dead along with his wife, 38, and two sons aged 9 and 13, in the state capital, Villahermosa, according to state Attorney General Rafael Gonzalez Lastra.
Fuentes Esperon was a former university rector, and was widely known in the state capital.
The state government immediately offered to provide protection for any candidate who wants it ahead of Oct. 18 elections.
Gonzalez Lastra said in a statement that President Felipe Calderon called Tabasco Gov. Andres Granier "to express his support and stress his decision to help in investigating the case to the end."
"There are no words to express these events. We are deeply moved and at the same time indignant," Gonzalez Lastra said.
The statement offered no information on the method or possible motive in the killings, but said they were carried out "with cruelty and viciousness."
Thousands killed since 2006
Local and state politicians have increasingly become victims of violence that has cost more than 13,500 lives since Mexico launched an offensive against drug cartels in late 2006.
Also Saturday, the army reported that five gunmen and a bystander were killed in a shootout at a lake that began when assailants opened fire on an army patrol on the outskirts of the northern city of Monterrey. One assailant and a bystander were wounded late Friday.
The army accused local police of protecting the gang and said it seized seven rifles, two grenades, and 10 notebooks naming "police personnel who offered information and protection." A kidnapping victim who spent a month in captivity was also freed.
The army said the gang — identified as members of the Zetas, a group of drug enforcers tied to the Gulf cartel — carried out kidnappings, extortions and drug sales.
"The military personnel exercised legitimate self-defense," an army statement said. "During the confrontation, a civilian who was in the recreation area with their family was killed ... and another was wounded."
More than 45,000 Mexican army troops have been dispatched to aid in the fight against drug cartels, and they have sometimes been accused of using their weapons indiscriminately.
In the northern state of Chihuahua, a severed human head was found placed on a car hood in the border city of Ciudad Juarez, along with a message relating to drug cartels, state prosecutors reported Saturday.
Ciudad Juarez municipal police reported that one of their officers was shot to death outside his home late Friday.
The federal attorney general's office reported Saturday that instructors of the U.S. Drug Enforcement Administration gave a course on drug addiction and prevention to federal and state prosecutors in Mexico. The course included instructions on organizing raids and other law enforcement activities, the office said in a statement.