The former presidential candidate of Mexico's leading leftist party is temporarily splitting with the group over a possible alliance with conservatives.

Andres Manuel Lopez Obrador says he has taken a "temporary leave" from the Democratic Revolution Party, or PRD.

PRD leaders recently decided to hold a referendum on whether to ally with President Felipe Calderon's National Action Party in July's Mexico state governorship vote.

Lopez Obrador contends that Calderon stole the 2006 presidential election by fraud.

He said Sunday in a statement that PRD leaders are betraying the party's principles. He did not specify whether he would permanently split, or seek the party's 2012 presidential nomination.