There are signs that key markets in this hemisphere are disrupted. There is evidence that there was a 9% decline in cocaine purity in the United States last year

John Walters, US drug czar

John Walters, drug czar in the Bush administration, said that by arresting key members of leading cartels Mexico had surpassed the anti-drugs efforts of the US.

"Mexico has done an outstanding job. The tempo and magnitude of disruption [to the cartels] and arrests of leaders of these organisations is like we have never seen before, in any country," he said on a visit to Mexico City.

"They are ahead of us in attacking the problem."

Walters called Mexico's crackdown 'historic'

Mr Walters said operations in Mexico had contributed to a drop in the quality of cocaine reaching the streets and a disruption to supply routes.

"There are signs that key markets in this hemisphere are disrupted. There is evidence that there was a 9% decline in cocaine purity in the United States last year."

Some experts say Mr Walter's comments underlined a new-found confidence in Mexico, where the conservative government of President Vicente Fox has promised to wage war on drugs.

Cartels' breakup

Mr Walters hailed Mexico's efforts as a historic crackdown after arrests earlier this year of suspected drug lords like Benjamin Arellan Felix and Jesus Albino Quintero.

Mexico is one of the main supply routes of cocaine to the US markets

"The closest I can think of is what happened in Colombia," he said, referring to a joint US-Colombian operation that resulted in the death of notorious drug lord Pablo Escobar in the early 1990s.

Mr Walters said the Mexican cartels were now being forced to break into smaller groups, while cash-flow problems made it difficult for them to pay Colombian suppliers when drugs were exchanged.

"The Colombians are not willing to provide drugs on a credit basis. They want cash."

But he also called for the widening of the drug battle against Colombian rebels and paramilitaries calling them "criminal gangs".