Opponents of Mexican presidential front-runner Enrique Peña Nieto pelted his motorcade with sticks and stones as the candidate was en route to a rally in the central state of Puebla.

The assailants blocked the road ahead of the convoy and then began hurling objects at the stopped vehicles, sources with Peña Nieto's Institutional Revolutionary Party, or PRI, told the media.

After a few minutes, the motorcade proceeded to the town of Tepeaca by an alternate route.

"It was an incident, not major, fortunately," Peña Nieto said later in an interview with Radio Formula. "But we have noticed, at various events in which I have participated, some groups of youths who are perhaps not numerous, but who have demonstrated an attitude that is a little hostile."

The attack on the motorcade came after partisans of the Yo soy 132 student movement confronted Peña Nieto in Izucar de Matamoros, Puebla, with anti-PRI placards, Milenio newspaper reported, adding that the candidate's supporters quickly wrested the signs away from the protesters.

Political tensions are rising in Mexico with the approach of the July 1 general elections.

Ulises Grajales Niño, PRI candidate for mayor of Villaflores, Chiapas, was arrested this week on suspicion of involvement in the murder of an activist from a rival party, while a woman running for a seat in the Guerrero state legislature was gunned down at her home.

Last Saturday, supporters and opponents of Peña Nieto came to blows during a soccer match at Mexico City's giant Aztec stadium.

PRI loyalists responded both verbally and physically when Yo soy 132 members in the stands started chanting anti-Peña Nieto slogans.

The student movement, which arose last month to demand that Mexico's television duopoly stop slanting campaign coverage in favor of the PRI, organized the protest via social networks.

Learning of the plans of Yo soy 132, the PRI chartered 60 buses to bring people from the central state of Mexico, where Peña Nieto was governor from 2005-2011, to the stadium for Saturday's contest.

The PRI also provided the passengers with tickets for the match, El Universal daily said. EFE