MEXICO CITY—Mexico fired nearly one-tenth of its entire Federal Police force en masse for failing lie-detector tests, being suspected of corruption, or for other reasons—a major blow to efforts to fight drug-trafficking gangs, The Wall Street Journal reports.

The purge of about 3,200 officers, which was carried out over the past week, is a blow to a relatively new force that is spearheading the country's crackdown on organized crime and is supposed to have been a model for a new kind of Mexican police officer.

While critics said the firings, the biggest in years in Mexico, were a sign of persistent rot in one of Mexico's more reliable law-enforcement institutions, others saw it as evidence that the government of President Felipe Calderón is committed to rooting out corruption.

Federal Police Commissioner Facundo Rosas told a news conference that the ousters were the result of screening tests administered throughout the force, including lie-detector exams, a toxicology test to determine drug use, and audits to see if an officer's income corresponded to his standard of living—a way to determine if an officer was engaging in lucrative illegal activity.

Mr. Rosas added that the dismissed officers would be barred from rejoining any police agency—a common problem when officials have purged police in the past.

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