Dirty campaigning mars Mexican election

MEXICO CITY - Mexico's political parties have agreed to play by the electoral rules in a close-run presidential race, but failed to restrain a fierce war of words between them that has marred campaigning.

The main parties vowed to follow regulations set out by the Federal Electoral Institute, signing a "civility pact" that may ease financial markets' worries of political gridlock and mass street protests if leftist candidate Andres Manuel Lopez Obrador disputes the result.

Lopez Obrador and conservative rival Felipe Calderon are running neck-and-neck for the July 2 election and investors fear the leftist, who has a long history of organising demonstrations, could refuse to accept the vote if he loses.

Today's agreement does not prevent parties from mounting legal challenges to the result if they believe fraud has taken place.

Even at a ceremony to sign the pact, Lopez Obrador's Party of the Democratic Revolution, or PRD, and Calderon's ruling National Action Party, or PAN, could not resist having a go at each other.

"The big challenge the Mexicans have in the 2006 electoral process is...to avoid the political transition failing and a return to state authoritarianism and irresponsible, demagogic populism," PAN chairman Manuel Espino said in a speech.

The PAN often accuses Lopez Obrador of being a populist like Venezuelan President Hugo Chavez.

"We reject all kinds of populism," PRD head Leonel Cota shot back. "Particularly the populism of the right."

An opinion poll in the Milenio daily showed Lopez Obrador ahead of his rival by three points. A poll by another newspaper on Monday had Calderon winning by the same margin and other surveys put the pair in a dead heat.

Electoral authorities have had to ban aggressive television adverts from both sides for libel.

- REUTERS