MEXICO CITY - Leftist presidential candidate Andres Manuel Lopez Obrador appears to be gaining ground on front-runner Enrique Pena Nieto ahead of Mexico's July 1 presidential election, according to new polls published Thursday, and analysts say student protests may be eroding his aura of invincibility.

A poll by the newspaper Reforma showed Lopez Obrador making a sharp climb over the past month. Pena Nieto led 29 per cent to 26 per cent in the late May poll, with a margin of error of about 3 percentage points. A month earlier, Pena Nieto had led the leftist 32-21.

A separate poll by the GEA/ISA firm showed front-runner Enrique Pena Nieto holding onto a stronger advantage, 33 to 21 per cent, with a 3 percentage point margin of error. That poll showed the leader down by three points and Lopez Obrador up by two since a similar poll taken two weeks earlier.

Both surveys showed ruling party candidate Josefina Vazquez Mota sinking toward third place. She had 18 per cent in the Reforma poll and 20 per cent in the GEA/ISA survey.

Reforma's poll showed about 32 per cent of voters undecided or without a preference, compared with 22 per cent in the GEA/ISA poll.

Student protests have dogged Pena Nieto's campaign over the last two weeks, with demonstrators who claim his Institutional Revolution Party, which held Mexico's presidency for 71 years, represents a return to Mexico's authoritarian past.

Those protests appear to be having an effect, said political analyst John Ackerman of Mexico's National Autonomous University, breaking the "aura of inevitability" that had hung over the campaign that Pena Nieto has led from the start.

"The election was somehow being portrayed as boring," Ackerman said. With Pena Nieto holding a lead of 15 to 20 per cent in polls in past months, there seemed to be little excitement until students took to the streets two weeks ago. Many denounced rights violations committed when Pena Nieto served as governor of Mexico State and many also warned against the return of his party.

"All of a sudden it's not boring," Ackerman noted.

"Pena Nieto is deflating," said Lopez Obrador, who had long run third in the polls. Many have considered him unelectable because of the angry, disruptive street protests he led following his narrow loss in the 2006 race to President Felipe Calderon. Lopez Obrador has sought this time around to soften his image, appeal to the middle class and businessmen, and apologize to those who were affected by his weekslong blockade of downtown Mexico City in 2006.

"Thanks to all the people who are trusting us," Lopez Obrador said at his daily press briefing Thursday. "They can be sure I am not going to betray the people. We are going to govern for all Mexicans." That was an apparent reference to his 2006 campaign slogan, "For the good of all, the poor come first," which he has since dropped in favour of a more inclusive slogan "for a loving republic"

Pena Nieto's campaign said it had no comment on the most recent poll numbers.

Aside from just hurting the front-runner, the student movement appears to be helping the leftist, whom many of its members support. The movement "hasn't come out publicly in favour of Lopez Obrador, but it doesn't have to," said political analyst Jose Antonio Crespo. "It is having an effect against Pena Nieto and for Lopez Obrador."

Ackerman predicted that, as the campaign tightens, "it may get pretty intense and possibly dirty."

Accusations are already emerging that the Pena Nieto campaign, stung by protests against it candidate, has orchestrated the appearance of small groups of protesters at its rivals' campaign events.

After a heckler got up on stage with Vazquez Mota at an even this week, she suggested the front-runner was behind the incident.

"If they are ahead in the polls as they claim, why do they send us provocateurs?" Vasquez Mota said after the man was shooed off the stage.

A spokesman for the Pena Nieto campaign refused to comment on those accusations.