Army troops killed four suspected drug traffickers in a shootout in Reynosa, a city in the northeastern state of Tamaulipas, the Mexican Defense Secretariat said.

The soldiers "were attacked with gunfire by an undetermined number of individuals" while on patrol in Reynosa, located across the border from McAllen, Texas, the secretariat said in a statement.

The four gunmen killed in the shootout have not been identified, the secretariat said.

The army seized four rifles, a handgun, a vehicle, ammunition clips and ammunition following the shootout.

"In a failed attempt to hamper and distract military personnel during the operations to neutralize the assailants, organized crime members staged a series of blockades on different streets in the cited city using vehicles, all of which were removed," the Defense Secretariat said.

The incident in Reynosa "is not linked in any way" to the surge in violence in neighboring San Luis Potosi state, the secretariat said.

The army is carrying out "Operation Northeast" in Nuevo Leon, Tamaulipas, Coahuila and San Luis Potosi in an effort to weaken the drug cartels that operate in the region.

The Gulf drug cartel has been waging a war in northeastern Mexico against Los Zetas, a band of army special forces deserters turned hired guns and drug traffickers.

After several years as the armed wing of the Gulf cartel, Los Zetas went into the drug business on their own account and now control several lucrative territories.

Violence has spiked this month in Mexico, with the Mexico City daily Reforma reporting on Saturday that 231 people were murdered across the country from Aug. 4 to Aug. 10, raising the death toll for the year to 6,309.

Edgar Morales Perez, a mayor-elect who belonged to the Institutional Revolutionary Party, or PRI, and an aide were murdered early Sunday in Matehuala, a city in San Luis Potosi state.

The other victim was Francisco Hernandez Colunga, who ran the politician's campaign, Mexican media reported.

A third man accompanying Morales Perez and Hernandez Colunga was not hurt in the attack.

San Luis Potosi was the scene last week of a grisly discovery.

A van containing 14 bodies was found Thursday on the outskirts of San Luis Potosi city, the state capital.

The victims were kidnapped in another state and taken to San Luis Potosi.

The van containing the bodies was found at kilometer 12 of the San Luis Potosi-Zacatecas highway.

The Federal Police killed three gunmen and arrested four others in an operation launched in the city following the discovery of the bodies.

More than 50,000 people, according to official figures, have died in drug-related violence in Mexico since late 2006.

The Movement for Peace with Justice and Dignity, which was founded by human rights activist and poet Javier Sicilia, puts the death toll at 70,000. EFE