Gunmen killed three municipal police officers in Ciudad Juarez, Mexico's murder capital, a police spokesman said.

The officers were traveling in an unmarked car Wednesday in Juarez, located across the Rio Grande from El Paso, Texas, when they were attacked by several gunmen who cut them off on a busy street, municipal police spokesman Adrian Sanchez said.

The vehicle was hit by more than 30 rounds fired from AK-47 assault rifles and hit a power pole.

Ciudad Juarez has been plagued by drug-related violence for years.

The murder rate took off in the gritty border city of 1.2 million people in 2007, when 310 people were killed, then it more than tripled to 1,607 in 2008, according to Chihuahua state Attorney General's Office figures, with the number of killings climbing to 2,754 in 2009.

More than 3,100 people were murdered in the border city last year, making 2010 the worst year since a war between rival drug gangs sent the homicide rate skyrocketing in 2008.

The killing has not slowed this year, with more than 1,000 people murdered in Juarez.

The violence is blamed on a war for control of the border city being waged by the Juarez and Sinaloa cartels with backing from hitmen from local street gangs.

At least 14,000 "armed criminals" are in Ciudad Juarez and Chihuahua city, the state capital, working for the drug cartels that are fighting for control of smuggling routes into the United States, Chihuahua Attorney General Carlos Manuel Salas said earlier this year.

About 5,500 of the armed criminals operating in Ciudad Juarez belong to Los Aztecas, a gang that works as the armed wing of the Juarez cartel, while the rest work for the Sinaloa cartel, Salas said.

The violence has not subsided in Ciudad Juarez despite the deployment of nearly 10,000 soldiers and Federal Police officers in the border city.

Mexico has been plagued in recent years by drug-related violence blamed on powerful cartels.

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

Calderon has deployed tens of thousands of soldiers and Federal Police officers across the country to combat drug cartels and other criminal organizations.