Authorities in Mexico detained a state official who got off a government-owned plane with a back and briefcase stuffed with $1.9 million, setting off allegations of campaign finance violations tied to the upcoming presidential election.

Tomás Ruiz, treasury secretary for Veracruz state, said there was nothing illicit about the money the official was carrying. He said the cash, from state coffers, was destined for a Mexico City advertising firm that agreed to promote festivals to attract tourists to the eastern coastal state, including a well-known carnival in the port city of Veracruz.

Ruiz said the Veracruz government had state official Miguel Morales Robles carry the cash payment on a special flight to Toluca airport outside Mexico City because the advertising work needed to be delivered quickly.

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Federal prosecutors said a second state official, Said Zepeda, was briefly detained Friday when he showed up at the airport to demand the release of his colleague and the money.

The two officials were released because there was no evidence they violated any law, but the money remains in prosecutors' custody.

Federal prosecutors said they were trying to confirm the money was from state coffers as part of the investigation. Ruiz said he had sent them documentation.

Veracruz state is governed by the Institutional Revolutionary Party, whose presumptive presidential candidate is considered the front-runner in the July election.

The Democratic Revolution Party, one of the PRI's two main competitors, charged that the money was meant to fuel a secret advertising budget for PRI candidate Enrique Peña Nieto.

The PRI has made strenuous efforts to rebrand itself as a law-abiding and transparent party that has left behind the legacy of corruption that marked much of its seven decades of autocratic rule, which ended with the 2000 presidential election.

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Mexico has strict limits on the amounts of money that can be spent on political campaigns — the PRI's presidential candidate will be limited to spending 495 million pesos ($38.4 million) for the entire campaign.

Political rivals routinely accuse each other of violating the limits, but electoral regulators rarely bring cases to prosecutors.

"We have before us, without a doubt, a diversion of state resources for the presidential candidate of the Institutional Revolutionary Party, Enrique Peña Nieto," the national leadership committee of the Democratic Revolution party said in a statement.

Ruiz strenuously denied that.

"The payment was in cash because of the rush," he told the news station Radio Formula when asked why he hadn't sent an electronic transfer.

With the start presidential campaign season in Mexico, government and party officials are warning about the potential for organized crime to get involved in campaigns and debating how to prevent that.

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Prosecutors wouldn't say if the money from Veracruz could possibly be linked to drug trafficking.

President Felipe Calderón last fall said that Veracruz, a state racked by drug violence, had been left in the hands of the Zetas drug cartel before he sent federal troops to restore order.

The state now is the center of a fierce battle between the Zetas and the Sinaloa cartel, Mexico's two most power drug trafficking organizations. Former Gov. Fidel Herrera was accused of being aligned with the Zetas, a charge he often denied.

Based on reporting by the Associated Press.

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