Updated

U.S. drug agents have uncovered evidence that cartel leaders paid millions to the governor of a Mexican border state and other members of Mexico's former ruling party in exchange for political influence, according to a court filing in Texas.

Four confidential informants told the Drug Enforcement Administration that Zetas and Gulf Cartel leaders made payments to members of the Institutional Revolutionary Party including Tomas Yarrington, who served as governor of the state of Tamaulipas in 1999-2004, according to a 13-page complaint filed in U.S. District Court in San Antonio, Texas.

The money-laundering conspiracy complaint against a man accused of funneling millions from the Zetas to Yarrington also says the DEA has obtained ledgers documenting millions of dollars in payments to Yarrington's representatives.

The U.S. investigation could have ramifications for Mexico's presidential race. The candidate of the Institutional Revolutionary Party, or PRI, has a big lead in opinion polls and has been expected to retake the country's most powerful office 12 years after the party was unseated at the polls after seven decades in power.

Yarrington did not respond to several requests for comment.

Mauricio Fernandez, head of the DEA's San Antonio office, described the complaint as the result of a lengthy and continuing investigation.

"It's an ongoing matter right now," he said. "A lot of people are working on this."

Mexican prosecutors said late last month that they were investigating former Tamaulipas officials in connection with unspecified federal crimes. Yarrington and two other former PRI governors, Manuel Cavazos and Eugenio Hernandez, acknowledged that they were subjects of the probe.

The PRI accused Mexico's governing National Action Party, its main opponent in the July election, of manipulating criminal justice for political ends.

The PRI's presidential candidate, Enrique Pena Nieto, appeared several days later at a rally in Tamaulipas hand-in-hand with Cavazos in a public show of support for the ex-governor, who is now running for a Senate seat.