WASHINGTON – Police in Texas urged U.S. citizens not to cross into Nuevo Laredo, a border city in the northeastern Mexican state of Tamaulipas, this weekend, citing reports that a drug cartel planned to attack Americans.

Los Zetas, considered Mexico’s most violent drug cartel, plans to attack Americans who cross the border during the Fourth of July weekend, the Texas Department of Public Safety, or DPS, and the Webb County Sheriff’s Office said.

“According to the information we have received, the Zetas are planning a possible surge in criminal activity, such as robberies, extortions, car-jackings and vehicle theft, specifically against U.S. citizens,” DPS director Steven C. McCraw said in a statement released on Saturday.

“We urge U.S. citizens to avoid travel to Nuevo Laredo this weekend if it can be avoided,” McCraw said.

Nuevo Laredo lies across the Rio Grande from Laredo, Texas, which is considered the “gateway to Mexico.”

About 11,000 trucks, as well as a constant stream of automobiles and families with relatives on both sides of the border, use the four international bridges linking Laredo and Nuevo Laredo every day.

Americans are drawn by the bars, restaurants and cheap dentists on the Mexican side of the border, but the flow of tourists has dried up over the past six years due to the surge in drug-related violence in Mexico.

“There is no indication that these cartel-related criminal activities will occur in Texas, but the DPS and Webb County Sheriff’s Office cannot discount the information received that supports possible crimes against U.S. citizens in Nuevo Laredo and perhaps the surrounding Mexican suburbs,” the law enforcement agencies said.

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

The violence intensified in the two border states after the appearance in Monterrey, the capital of Nuevo Leon, 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.