Mexican voters head to the polls on Sunday to elect governors in the states of Mexico, Coahuila and Nayarit.

Early opinion polls indicate candidates of the Institutional Revolutionary Party are leading candidates from President Felipe Calderon's conservative National Action Party .

The PAN has attempted to partner with the leftist Democratic Revolution Party to defeat the PRI in Nayarit and Coahuila, but its candidates are still favored in those races Sunday.

The PRI's current governor in Mexico state, Enrique Pena Nieto, is considered a front-runner in next year's presidential race. Mexico is the country's most populous state.

Pena Nieto could face President Calderon, who analysts suggest may be vulnerable for a defeat in 2012 because his country's escalating drug violence has diminished his popularity and the influence of his party.

Tens of thousand of people have died in drug violence since Mr. Calderon took office in 2006 and began a campaign against the drug cartels.