Gunmen left a live man hanging from a heavily used bridge in Monterrey, the capital of the northern state of Nuevo Leon and one of the cities most affected by drug-related violence in Mexico, and dumped a body nearby, officials said.

Unidentified individuals traveling in two vehicles stopped on a ramp at the busy intersection of Avenida Revolucion and Chapultepec on Wednesday and strung up a live man off a bridge by his hands and tossed a dead body into the roadway.

A gunman returned to the bridge and fired several shots with an assault rifle at emergency services workers who tried to take the man down.

Army troops, Federal Police officers and state police arrived on the scene, allowing emergency services personnel to finally get the man down and recover the dead body.

The man rescued by first responders had a radio frequency device tied to his hands along with a message from the Gulf drug cartel for the informants employed by the rival Los Zetas gang.

The violence continued a few hours later in Teran, a rural city about 90 kilometers (56 miles) south of Monterrey, where four men were gunned down at a car wash by assailants armed with AR-15 assault rifles.

Matias Salinas, 23, Edgar Jair Flores Cano, 20, Silverio Pineda Gaytan, 35, and his son, David Pineda Torres, 17, died in the attack, officials said.

Nuevo Leon and neighboring Tamaulipas state have been rocked by a wave of violence unleashed by drug traffickers battling for control of smuggling routes into the United States.

More than 1,100 people, including about 80 police officers, have died in the violence in Nuevo Leon in the past year.

The violence intensified in the two border states after the appearance in Monterrey in early 2010 of giant banners heralding an alliance of the Gulf, Sinaloa and La Familia drug cartels against Los Zetas.

Heriberto Lazcano Lazcano, known as "El Lazca," deserted from the Mexican army in 1999 and formed Los Zetas with three other soldiers, all members of an elite special operations unit, becoming the armed wing of the Gulf drug cartel.

After several years on the payroll of the Gulf cartel, Los Zetas, considered Mexico's most violent criminal organization, went into the drug business on their own account and now control several lucrative territories.

A total of 15,270 people died in drug-related violence in Mexico last year, and nearly 40,000 people have died since President Felipe Calderon declared war on the country's cartels shortly after taking office in December 2006.