Garza's comments were included in a letter directed to Foreign Relations Secretary Luis Ernesto Derbez and federal Attorney General Rafael Macedo de la Concha that explained the motives behind Wednesday's warning from the U.S. State Department to citizens thinking of traveling to the region. The U.S. Embassy in Mexico distributed the letter to news agencies.

Interior Secretary Santiago Creel told a news conference late Wednesday that Mexico "is determined to wage a head-on battle" against drug traffickers and organized crime groups operating on the border. The United States is aware of Mexico's efforts, he said.

"We are going to succeed," he said, adding that federal officials have received the commitment of all of Mexico's state governments in the north.

Derbez did not comment immediately.

Violent criminal activity, including killings and kidnappings, has increased in the northern border region amid a growing war between drug traffickers struggling for control of the region.

"U.S. citizens should be aware of the risk posed by the deteriorating security situation," the State Department warning said.

The advisory came just days after the Mexican government sent soldiers to patrol the streets of the border city of Nuevo Laredo, across from Laredo, Texas, at the request of local authorities who said the crime and violence had become too great for them to handle.

It also comes as officials crack down on top-security federal prisons housing reputed drug traffickers who allegedly have continued to operate their businesses from behind bars with the help of corrupt prison employees.

Garza noted that while the great majority of border violence victims are Mexican citizens, "the elevated level of violence generally has resulted in greater risks to the thousands of U.S. citizens visiting and passing through the border region every day. Increased numbers of murdered and kidnapped Americans in recent months bear this out."

Garza went on to say that he worried "the inability of local law enforcement to come to grips with rising drug warfare, kidnappings and random street violence will have a chilling effect on the cross-border exchange, tourism and commerce so vital to the region's prosperity. ... We certainly do not want at this time to advise U.S. citizens to refrain from traveling to Mexico by land or to avoid the border areas, but it is our responsibility to alert them to the enhanced risks," Garza said, explaining the motive for Wednesday's warning.

He added that he applauded President Vicente Fox's efforts to combat crime and drug trafficking and said he hoped "that commitment will make a difference at the state and local levels."

Creel, meanwhile, recognized Garza's offer to provide additional U.S. cooperation in the fight against organized crime groups in Mexico. "We appreciate" the offer, he said.

The U.S. consul to Reynosa, on the Mexican border across from McAllen, Texas, issued a separate warning in September for U.S. travelers planning to visit that city. The advisory came after reports that Mexican police allegedly were forcing U.S. drivers to remote places or to automated cash machines, where they were told to hand over money or face jail time.

That warning prompted Reynosa Mayor Francisco J. García Cabeza de Vaca to defend his city in a news conference last week.

Garza acknowledged the strides that have been made thus far to improve security on the border, and said, "I hope this current challenge can be faced with similar resolve and success."