Mexican officials attending a security conference this week in El Paso, Texas, expressed concern about rising drug use and the drug-related violence in Mexico.

"I have heard much concern with relation to the violence in Mexico and I can assure you that Mexico is working tirelessly against organized crime," the Mexican Attorney General's Office representative in El Paso, Hugo Ernesto Gonzalez Salinas, said.

"What we are concerned about now is what we are going to do about the drugs ending up in Mexico due to the success of efforts by both governments to stop the flow of drugs into the United States," Gonzalez Salinas said.

Drug use in Mexico, when viewed in a historical context, has increased in the past few decades because of economic growth that made it possible for people to afford to buy narcotics, Mexican federal security spokesman Alejandro Poire said.

"The (drug) consumption in Mexico is worrisome, but it is not comparable to consumption in the United States," Poire said.

Mexico's drug cartels have expanded their power in the past 10 years, thanks to cocaine trafficking from South America to the United States, Poire, who serves as Mexican National Security Council technical secretary, said.

The officials attending the conference, which wrapped up on Tuesday, also discussed illegal immigration.

Detentions of undocumented migrants on the border have fallen dramatically, with arrests expected to be down 46 percent by the end of the current fiscal year on Sept. 30, U.S. Customs and Border Protection Commissioner Alan Bersin said.

The situation in Arizona is of concern now because the flow of migrants is shifting there due to the tightening of security around El Paso, located across the Rio Grande from Ciudad Juarez, Mexico, Bersin said.

Regardless of the party that wins Mexico's 2012 presidential election, the United States will continue cooperating in the war on drugs under the framework of the Merida Initiative, Assistant Secretary for the Bureau of International Narcotics and Law Enforcement Affairs William Brownfield said.

The Merida Initiative is a $1.4 billion security cooperation pact aimed at fighting drug trafficking and other forms of transnational organized crime.

"I want to make this clear, it does not matter if it is the PAN, the PRI or another party that wins the elections, the initiative will continue working, even if it undergoes some minor adjustments," Brownfield said.

The flow of high-powered rifles into Mexico has increased markedly in recent years, Robert Champion, special agent in charge of the Dallas Field Division of the Bureau of Alcohol, Tobacco, Firearms and Explosives, said.

Champion defended "Operation Fast and Furious," a U.S. operation that allowed thousands of firearms to be smuggled into Mexico and is under investigation.

"We (ATF) were criticized because we only focused our efforts on attacking the suppliers of these weapons and when we wanted to expand our efforts and attack the criminal organizations, it worked out badly," Champion said.