May 27--REPORTING FROM MEXICO CITY -- Cancun would rather be known for powdery beaches and Windex-blue waters, but on Wednesday it was the scene of an explosive corruption scandal: Did its mayor secretly work on behalf of two of Mexico's most bloodthirsty drug-trafficking organizations?

The charges against Mayor Gregorio Sanchez, who is on leave to run for governor of the state of Quintana Roo, add new force to worries that organized crime groups have infiltrated Mexican politics at all levels and are undermining the country's fragile moves toward a real democracy.

Sanchez, who cultivated the image of a populist, anti-corruption mayor, was arrested late Tuesday night at Cancun's airport on suspicion of involvement in organized crime, money laundering and making transactions using illegal proceeds.

He is the most visible elected figure arrested on drug-related charges since President Felipe Calderon launched his war against traffickers 3 1/2 years ago.

Federal authorities on Wednesday said Sanchez provided information and protection to two feared groups -- the Zetas and the Beltran Leyva gang -- to help them ply their trade in the region. Officials found that Sanchez, a successful former resort builder in his early 40s, was moving funds through his accounts in sums far bigger than his reported income of $1.5 million, said Ricardo Najera, spokesman for the federal attorney general's office.

An amateur singer, the clench-haired Sanchez won support from many Cancun residents for firing corrupt police officers, and he likes to boast of his public works projects, including turning trash-strewn lots in scruffy neighborhoods into parks.

Sanchez, who was endorsed by a coalition of leftist parties, is the first person in recent memory to be arrested in the midst of a gubernatorial campaign in Mexico. Early polls showed him trailing in Quintana Roo, one of 14 states that will hold elections July 4.

Supporters from Sanchez's opposition Democratic Revolution Party, or PRD, charged that the arrest was an election-season stunt by the conservative government of Calderon to deny Sanchez Quintana Roo's top office.

On Tuesday, hours before his arrest, Sanchez charged that he was being threatened and targeted by political foes as part of a "dirty war."

Sanchez, who was elected mayor in 2007 and goes by "Greg," used Twitter to announce that he had been detained at Cancun International Airport late Tuesday night, saying he was being held "illegally." Numerous tweets sent from his Twitter account on Wednesday took aim at the accusations.

"Why now? Because we're winning," one said. It was not immediately clear who was sending the messages under his name.

Sanchez's supporters disparaged the arrest as a "Michoacanazo," referring to the Calderon government's arrests during last year's election season of more than two dozen public officials -- mostly from the PRD -- in the western state of Michoacan for alleged ties to organized crime. Nine of the 10 mayors arrested were later freed for lack of evidence.

"This is a political prosecution. There is no other word for it," Sanchez's wife, Niurka Saliva, told reporters.

Najera, who said some of the evidence against Sanchez came from confidential witnesses, denied political considerations.

Jesus Ortega, the PRD's president, said Sanchez's campaign would go on.

The nation's escalating drug violence has already cast a long shadow over the 2010 campaigns, with a mayoral hopeful shot dead this month in northern Mexico and some possible candidates too afraid to run for office.

In the northwestern state of Sinaloa, a well-known trafficking center, suspicions have swirled around a gubernatorial candidate, Jesus Vizcarra, after a newspaper published a photograph that showed him at a party many years earlier with suspected drug lord Ismael Zambada.

"It's hurting the democratic process," said Alberto Islas, a security analyst in Mexico City. "Instead of being a contest about what people really want ... you have to choose between who is the bad guy and who is not the bad guy."

Rumors about Sanchez's possible ties to organized crime had been circulating strongly for months in Cancun, a city of about 750,000 with a hidden, gritty underside and a long history as a hotbed of drug sales and smuggling.

Three Sanchez associates, including the city's police chief, were arrested last year in connection with the assassination of a retired army general, Mauro Enrique Tello, who had begun work as Sanchez's security advisor.

In an interview with The Times two weeks after the killing, Sanchez said he had hired Tello to clean up the resort city's corrupt police. Tello and two other men were found dead, riddled by bullets, on Feb. 3, 2009, next to a highway outside Cancun. His arms and legs had been broken.

"We're putting things in order," Sanchez said at the time. "We want to clean house."

The Tello slaying hasn't been solved.

Cancun, perched along the Caribbean with a glistening international airport, occupies a strategic spot for smuggling cocaine from South America to the United States. Plus, hundreds of thousands of foreign tourists each year offer a robust market for illegal drugs.

A former Quintana Roo governor, Mario Villanueva Madrid, was extradited to the United States this month to face U.S. charges that he took millions of dollars in bribes to help the Juarez cartel smuggle cocaine while he held office during the 1990s. He was arrested in 2001.

Islas, the security analyst, said Sanchez's arrest could trigger jostling between traffickers if the Cancun market is now seen as up for grabs. "It could lead to violence," he said.

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