MEXICO CITY (Reuters) - Corrupt officials inside Mexico’s security forces have leaked U.S. anti-drugs intelligence directly to drug traffickers to help them escape raids, a senior U.S. law enforcement agent said.

Mexican federal police escort away members of a detained drug trafficking gang after a news conference in Mexico City October 19, 2008. REUTERS/Daniel Aguilar

A recent anti-corruption sweep showed the infiltration of Mexican police forces had reached alarming levels, with several high-ranking investigators and a presidential guardsman arrested for selling information to drug cartels.

The U.S. agent said the arrests were an encouraging sign that Mexico’s government is serious about stopping drug gangs from getting their hands on intelligence, some of which comes from the U.S. Drug Enforcement Administration, or DEA.

“There have been occurrences where we have shared information and then found that the information we shared was compromised, given, provided, leaked to the very targets that were being investigated,” the official told Reuters late on Wednesday on condition of anonymity.

Mexican President Felipe Calderon has made fighting drug cartels his top priority, deploying thousands of soldiers and federal police to take on heavily armed traffickers, dominated by the Sinaloa federation and the Gulf Cartel.

The U.S. agent praised Calderon for fighting the drug gangs head on but said some operations have been frustrated as cartels flush with cash can pay massive bribes for information or use violence to intimidate police.

“There is no infallible system when you are talking about a $65 billion enterprise. Money talks,” he said, referring to the estimated size of Mexico’s drug trade.

Among those arrested last year were Mexico’s liaison to Interpol as well as the country’s organized crime chief Noe Ramirez, who is accused of taking at least $450,000 to pass secrets to crime gangs.

Mexican investigators could not comment on leaks of DEA information to cartels, a spokesperson from the attorney general’s office said on Thursday, but one expert said it was a worrying sign.

“This could have consequences in bilateral cooperation if the United States becomes less willing to share information with Mexico. We are facing a crisis of confidence,” Jorge Chabat at Mexico’s CIDE think tank said.

U.S. AID IN DRUG FIGHT

The U.S. Congress approved $465 million in drug-fighting aid for Mexico and Central America in June, the first installment of a promised $1.4 billion package known as the Merida initiative to fund surveillance and detection.

“Merida recognizes that there is this level of corruption, so the point is to tighten up the institutional capabilities,” University of Miami drug expert Bruce Bagley said, adding that U.S. aid will help in vetting Mexican forces.

“They will have urinalysis kits and lie detector tests ... they will also interdict government officials’ phones, check out their bank accounts, because there has to be enhanced monitoring of all of the highest levels,” Bagley said.

But even specially selected police units working directly with the DEA are not always immune to corruption.

“With the specialized units, in effect, we are operating on islands of integrity in a sea of questions, but there are breaches from time to time,” the U.S. official said.

Some 5,700 people died in drug-related killings in Mexico last year as drug gangs battled each other and government security forces, and the U.S. agent said violence has begun to spill over the border into the southern United States.

“I believe if we don’t turn around and do something we could see a tremendous degradation of security in our own country from these trafficking organizations,” he said.