More heroin, marijuana from Mexico

WASHINGTON (Reuters) - Mexican cartels, the biggest source of illegal drugs to the United States, have increased the flow of heroin, marijuana and methamphetamines and have become even more powerful, the U.S. Justice Department said on Thursday.

Mexican traffickers grew especially strong in some eastern U.S. markets as Colombian drug rings weakened, according to a report by the National Drug Intelligence Center.

The center, part of the Justice Department, estimated the U.S. economic cost of trafficking and abuse of drugs at $215 billion annually and said Mexico continued to pose the single greatest drug trafficking threat to the United States.

The unit, the nation's main center for drug intelligence, said Mexican cartels are the only drug traffickers operating in every region of the United States and they have increasingly joined forces with American street and prison gangs.

These alliances expanded drug operations from cities into the countryside and suburbs, the report said.

The United States is deeply involved in Mexico's battle against drug gangs, pledging $1.4 billion over three years to fighting the cartels that ship $40 billion worth of illegal drugs north each year.

Mexico's drug violence has become a major political test for President Felipe Calderon and a worry for Washington, foreign investors and tourists as violence has spread across the Southwest border.

Two Americans were killed in a shooting this month in the Mexican border city of Ciudad Juarez.

The report said the cartels have increased the flow of heroin, methamphetamines and marijuana into the United States, primarily reflecting increased production in Mexico.

But cocaine shortages have persisted in many U.S. drug markets for the past few years, primarily because of decreased cocaine production in Colombia and increased worldwide demand.

Stepped-up Mexican government efforts also have helped cut down on Colombian cocaine smuggled into the United States.

The report said Mexican drug traffickers associates buy thousands of weapons each year in Arizona, California, and Texas and smuggle them into Mexico.

"This report presents a comprehensive analysis of the drug threat to our nation and will be valuable in helping direct our fight against drug trafficking and abuse," Attorney General Eric Holder said in a statement.

(Editing by Doina Chiacu)