Mexico's ruling party blasts ex-president for backing rivals

The National Action Party (PAN) issued a statement urging Fox, who swept the PRI from power in a historic 2000 election and served as president until 2006, "not to betray democracy" after he said the country must rally around the likely winner of the July 1 presidential contest.

PRI candidate Enrique Pena Nieto is leading in polls with the PAN's contender Josefina Vazquez Mota slipping into third place in most surveys.

Creeping ahead of Vazquez Mota, with less than a month to go before the election, is leftist and 2006 runner-up Andres Manuel Lopez Obrador.

Lopez Obrador lost the last election by less than one percentage point to President Felipe Calderon and contested the results, declaring himself the legitimate president of Mexico and maintaining a public presence for the past six years.

He is now firing up his old supporters and a new generation of young voters opposed to Pena Nieto's candidacy and gaining on the frontrunner.

Vazquez Mota has been forced to step up attacks on both Pena Nieto and Lopez Obrador and Fox's comments are likely to only add to her troubles.

Without naming Pena Nieto directly, Fox said "a clear winner is emerging."

"We have to achieve unity. We are losing ground compared to other countries and we cannot go on like this, we have to close ranks behind who will win," he told reporters.

Fox ended seven decades of PRI rule when he swept to power 12 years ago. The PAN held onto the presidency with Calderon's election in 2006 but failed to win a majority in congress, stalling the party's reform agenda.

The PAN says a vote for Pena Nieto will be a step backwards to the days when a single-party rule when the PRI held power with a savvy combination of patronage and corruption.

"Fox shouldn't forget that he is responsible for the change that ended decades of authoritarianism and economic and political backwardness in Mexico," said PAN party president Gustavo Madero in a statement.

"So it is incongruous, contradictory and absurd that he is promoting a vote for a party that represents everything he stood against in 2000," Madero said.

Calderon is legally barred from running for re-election and Vazquez Mota - aiming to become Mexico's first woman president -has struggled with party infighting since she won a contested primary race in February.

Fox in previous statements has said it would be a "miracle" if Vazquez Mota won the race.

(Reporting by Mica Rosenberg; Editing by Cynthia Osterman)