Mexico temporarily removed all 284 of its top federal police officers from their jobs and is forcing them to prove they will not be corrupted in the fight against drug trafficking, the government announced Monday.

Mexican authorities often have purged police forces in attempts to eliminate corruption, only to see the fired officers go to work full time for organized crime. This is one of the most extreme measures taken yet in hopes of guaranteeing the honesty of high-ranking officers.

It comes as Mexico seeks more U.S. aid in its crackdown on drug gangs. Washington has long complained about endemic corruption hindering anti-smuggling efforts in Mexico, but Public Safety Secretary Genaro Garcia Luna said the review came in response to Mexican frustration over corruption, and has nothing to do with U.S. pressure.

In recent years, scores of federal police have been caught working for the drug cartels, tainting what Mexicans once considered their last trustworthy group of officers.

"We are well aware that the Mexican people are demanding police be honest, clean and trustworthy," Garcia Luna said. "It's obvious that there are mafias that don't want the situation to change so they can continue to enrich themselves under the protection of corruption and crime."

Garcia Luna said the 284 high-ranking police would be forced to undergo what he called a "trust test" including anti-doping exams, polygraphs and psychological reviews; investigations of their acquaintances, friends, and family; and checks on whether their assets are in line with their earnings.

Garcia said the 284 officers would keep their ranks while undergoing the evaluation, and the 34 with the best results will be promoted to regional federal police chiefs, the highest positions in the field. Those who flunk the drug and polygraph tests will be off the forces.

A separate group of 16 officers have been ordered to take courses on professionalism after failing initial tests, and six others who refused drug tests will be turned over to internal affairs, Garcia Luna said.

The government wants to avoid firing officers because after past purges officers have gone on to help organized crime improve their communications, weaponry and techniques, officials have said.

The 284 officers are prohibited from speaking publicly until the investigation is completed.

U.S. officials also have recommended that Mexico streamline its tangle of federal police forces, which often compete with each other and refuse to share information. This evaluation focuses on the Federal Preventative Police and the Federal Agency of Investigation, or AFI, which are leading the drug fight with soldiers.

President Felipe Calderon's predecessor, Vicente Fox, created AFI, which is equivalent to the U.S. Federal Bureau of Investigations, shortly after taking office in December 2000 as a replacement for the notoriously corrupt and inept Federal Judicial Police.

But AFI has not been without its problems: In one of the most infamous federal police corruption cases, regional AFI director Armando Villalobos was arrested along with 26 other officers in Cancun in 2004. The arrests were for the deaths of seven people, including three federal agents, in violence linked to a ring that paid police to protect drug smugglers.

State and local police also are suspect. In April, the Nuevo Leon state government arrested an unprecedented 141 state officers, accusing them of working for the powerful Gulf cartel along the Texas border. And in Tijuana earlier this year, soldiers patrolled the streets while local police were disarmed following accusations they protected smugglers.

In a rare acknowledgment of the gravity of violence related to drug trafficking, Mexico's top domestic security official, Interior Secretary Francisco Ramirez, recently said the government had lost control before President Felipe Calderon launched the current offensive.

The heavily armed drug gangs are blamed for more than 1,300 deaths this year, including dozens of decapitations. Calderon responded by sending out more than 24,000 soldiers and federal police to battle the traffickers, and by ordering the creation of an elite military special operations force capable of surgical strikes.

The Calderon administration insists the crackdown is working. More than 1,000 gunmen have been detained, and millions of dollars in marijuana plants burned. Traffickers are being extradited to the U.S. more rapidly than ever before, and police recently made the world's biggest seizure of drug cash, US$207 million (euro153 million) neatly stacked inside a Mexico City mansion.

U.S. Drug Enforcement Administration officials say its too early to judge the crackdown's success, and U.S. drug seizures indicate the flow across the border may be increasing.