A top adviser to Andrés Manuel López Obrador, the leftwing candidate in Mexico's presidential election, yesterday sent the strongest message yet that his party would seek to annul Sunday's vote.

Manuel Camacho, a congressman for Mr López Obrador's Democratic Revolution Party (PRD) and a key strategist in the leftwing candidate's campaign, told the FT yesterday: "We are almost certainly going to contest this election . . . but we are not going to generate a dispute unless we are sure of our arguments."