MEXICO CITY (AP) — Mexico accused its former drug czar Friday of taking $450,000 from a cartel he was supposed to destroy, going public with a scandal that deals a serious blow to the country’s U.S.-backed drug war.

Noe Ramirez is the highest-ranking law enforcement official detained yet as part of Mexico’s sweeping effort to weed out officials who allegedly shared police information with violent drug smugglers. The corruption scandal is the biggest to rock the Mexican government in more than decade.

Although the arrest complicates President Felipe Calderon’s nationwide crackdown on the drug trade, Attorney General Eduardo Medina said it also proved the government’s commitment to rooting out corruption.

That commitment could be key to ensuring continued U.S. support for its drug fight. The U.S. Congress conditioned 15 percent of a still-to-be-released $400 million aid package on Mexico’s efforts to clean up its police force.

U.S. investigators work closely with their Mexican counterparts, sharing information with those who have been closely vetted. The Drug Enforcement Administration hasn’t said if it plans to pull back on cooperation, given the questions surrounding whom to trust.

But Thomas Schweich, a former U.S. deputy assistant secretary of state for international law enforcement, said the revelations suggest Mexico is aggressively dealing with its corruption problem.

“I find the whole situation encouraging. If you are a corrupt official, you are no longer immune to prosecution no matter how high up you are,” said Schweich, who now works for the Bryan Cave law firm in St. Louis. “It shows a lot of political will on the part of Calderon.”

For many in Mexico, the government’s very public admission of the problem was more surprising than the allegations themselves. Friday’s news conference provided a rare glimpse into details of how cartels allegedly bought off top officials.

Medina said Ramirez accepted $450,000 from a member of the Pacific cartel, who offered to pay him similar amounts each month for alerting the drug gang to planned police operations. It was unclear if the subsequent payments were ever made. The cartel member is now cooperating with investigators, Medina said.

Ramirez was named assistant attorney general for organized crime in 2006 when Calderon took office, and resigned in July at Medina’s request. No corruption allegations were raised at the time — federal officials said his resignation was part of a law enforcement shake-up by the Calderon administration.

Ramirez was helping to lead Calderon’s nationwide offensive to take back territory controlled by drug cartels, a two-year campaign involving the deployment of more than 25,000 army troops and federal police.

Calderon has long acknowledged that corruption is an obstacle for his offensive, which has resulted in several kingpin arrests but failed to contain rising violence that includes drug gangs decapitating their rivals and staging daylight attacks on police and soldiers.

“The Mexican government is strongly committed to fighting against not only organized crime but the corruption that organized crime generates, and that has become entrenched over years and perhaps decades in the structures of power,” Calderon said while traveling in Chile on Friday.

The offensive won strong support from the Bush administration, which pushed hard for congressional approval of the aid package to provide Mexico with planes, helicopters and training for the drug war. U.S. lawmakers had hesitated to approve the so-called Merida Initiative because of concerns of human rights abuses by soldiers and corruption.

With the arrest of Ramirez, at least five top officials and two federal agents have been detained this year as part of “Operation Clean House,” which targets officials who allegedly shared information with the Pacific cartel, an alliance headed by the Sinaloa drug gang.

Officials haven’t said what information was leaked, but the suspects had access to critical, actionable intelligence about the government’s moves against the cartels. They include Gerardo Garay, the acting chief of Mexico’s federal police, who resigned and is under house arrest. Officials have not detailed charges against him, and he has denied any wrongdoing.

The scandals are the most serious since the 1997 arrest of Gen. Jesus Gutierrez Rebollo, who led Mexico’s anti-drug agency and was later convicted of aiding a top drug lord.

The investigations are likely only to reinforce the mistrust most Mexicans harbor against police, long believed to be involved in drug trafficking at all levels. Only a year ago, Mexico replaced all its top federal police officers in a confidence-building effort.

The government also promised then that senior officers would be subject to an arduous screening, including polygraphs and checks on whether each officer’s assets are in line with earnings.

Medina said the government remains determined to identify those who “are involved in criminal activities and have abandoned the principles and values of public service.”

Medina said Ramirez met twice with his Pacific cartel contact in Mexico City, and brought two other directors of his agency’s organized crime division to the second meeting. They also were arrested. Ramirez is in jail pending an investigation on possible charges of involvement with organized crime.