President Felipe Calderon's National Action Party, or PAN, said in letters sent to Nuevo Leon Gov. Rodrigo Medina and Monterrey Mayor Fernando Larrazabal that they should leave their posts so that the probe into last month's deadly casino arson attack doesn't become "a struggle between political forces."

Larrazabal is a member of the PAN but Medina belongs to the opposition Institutional Revolutionary Party.

Larrazabal's brother, Jonas, has been detained for questioning in a casino-related corruption probe after videotapes became public showing him taking wads of cash inside an unidentified casino just days before the fire in the Casino Royale.

The newspaper Reforma, which published the images of Jonas Larrazabal, estimated that one wad of cash, stuffed inside a cell phone box, contained 400,000 pesos ($32,000). Reforma reported that Jonas had visited at least three casinos to collect money in the weeks before the August 25 fire.

Jonas Larrazabal's lawyer, Jesus Martinez, has said that his client goes to casinos for fun, like any customer, but also sells them cheese, mezcal and other products from the southern state of Oaxaca.

Fernando Larrazabal told Multimedios television in Monterrey he would consider his party's suggestion to step down and announce a decision on Wednesday.

"I was backed by National Action but those who chose me were the people of Monterrey," he said.

The party said Medina should also step down so authorities can investigate whether officials in his administration are working with organized crime.

This request is justified by "the obvious support state police officers gave to the criminals that set fire to the Casino Royale," the PAN said referring to the arrest of a state police officer in the case.

The state police agent was caught in a surveillance video inside an SUV outside Casino Royale, presumably connected to the attack.

Authorities say five others arrested in the case confessed to being members of the Zetas drug cartel. Authorities are investigating the crime as a presumed extortion attack by the gang.

A cable from the U.S. consulate in Monterrey, obtained by WikiLeaks and dated July 2009, said two brothers who are the largest casino operators in Monterrey's metropolitan area illegally donated US$2.5 million each to Adalberto Madero, the former mayor of Monterrey and a PAN member, and Zeferino Salgado, the current PAN mayor of San Nicolas and the PAN's candidate for federal congressman for the San Nicolas congressional district.

"In addition to campaign contributions, Madero and Zeferino are said to also receive a monthly percentage of the revenue from the casinos," the cable said.

Salgado, who is now a transportation ministry official, denied the accusation.