Attorney General Eric Holder: They have shown incredible ruthlessness
More than 300 people have been arrested in a series of drug raids targeting a Mexican drug cartel operating in the US, American officials have said.
The two-day operation, which involved thousands of police officers in 19 US states, is the latest aimed at the cartel known as La Familia.
It was part of Project Coronado, which has led to almost 1,200 arrests over four years, officials said.
The US attorney general said the cartel had been dealt a "significant blow".
La Familia, which is based in the western Mexican state of Michoacan, has been accused of carrying out bloody attacks on Mexican security forces.
Mexico's President Felipe Calderon has deployed more than 45,000 troops to fight drug gangs since he took office in December 2006.
However, more than 11,000 people have been killed in drug-related violence in that time.
Announcing the arrest of 303 suspected cartel members on Thursday, Attorney General Eric Holder described the gang as demonstrating "an incredible level of sophistication and ruthlessness".
Previously believed to answer to Gulf Cartel, listed as separate group in March 2009 government report
Combines code of violence with idea of protecting people in Michoacan from outsiders
Also involved in counterfeiting, extortion, kidnapping, armed robbery, prostitution, protection rackets
He said the raids had disrupted the cartel's operations, which "stretch far into the US".
"This operation has dealt a significant blow to La Familia's supply chain of illegal drugs, weapons and cash flowing between Mexico and the United States," he said.
Mr Holder praised the Mexican government for its "heroic" efforts to combat drug trafficking, saying it was "not a one-country problem and solving it will take more than a one-country solution".
The Mexican authorities "face a problem of almost unimaginable dimensions", he added.
In the course of the two-day crackdown, US police and FBI agents seized $3.4m (£2.05m) in cash, 144 weapons and more than 100 vehicles, as well as stashes of methamphetamine, cocaine and marijuana.
"These are drugs that were headed for our streets, and weapons that often were headed to the streets of Mexico," Mr Holder said.
FBI Director Robert Mueller said La Familia had transformed in recent years "from a drug cartel to a sophisticated criminal organisation".
A grand jury in New York has indicted an alleged leader of La Familia, Servando Gomez-Martinez, and three other suspected gang members on charges of conspiracy to import cocaine and methamphetamines.
Police parade alleged drug cartel members in front of TV cameras