Firefighters stand amidst smoke coming out from a building housing a casino after an attack in Monterrey. Armed men killed at least 51 people in an attack on a casino in northern Mexico that left the building ablaze with gamblers trapped inside, officials said on Thursday.

Monterrey, Mexico - The brother of the mayor of Monterrey, in northern Mexico, has been provisionally detained after pictures published in the press showed him receiving bundles of cash from city casinos.

The detention came a week after an arson attack on Monterrey's Casino Royale which left 52 people dead, and which authorities linked to extortion.

Jonas Larrazabal, brother of mayor Fernando Larrazabal, was detained late Thursday in a probe into corruption and organized crime and could be held for up to 30 days.

The prosecutor of Nuevo Leon state, Adrian de la Garza, told a news conference Friday that Larrazabal was being held for suspected crimes.

“I'm not saying he committed those crime, but there's a presumption,” he said.

Reforma daily on Wednesday and Thursday printed photos, taken from a security camera, of Larrazabal receiving bundles of cash in several casinos, and of one of them being vandalized, purportedly in an extortion attempt.

Although no formal link has been made between the casino attack and the videos, some politicians and business leaders have called for the resignation of Monterrey's mayor over the case.

“I can't be responsible for the actions of my brother,” the mayor told journalists this week.

President Felipe Calderon condemned the attack in his annual address to the nation Friday and called for scores of poorly-regulated casinos to be investigated, as well as “possible cases of corruption ... whomever they concern.”

A police officer and five suspected members of the Zetas drug gang have so far been detained in the probe into the arson attack on the Casino Royale. - Sapa-AFP