Mexican congressmen yesterday voted to hold an impeachment trial of Andrés Manuel López Obrador, the leftwing mayor of Mexico City who leads polls for next year's presidential election, in a move that dramatically raises political tensions in the country.

Three of the four members of the congressional rules committee agreed the case against the mayor should go to trial, with the lone dissenting vote coming from the mayor's Democratic Revolution party (PRD). Horacio Duarte, the party's representative on the committee, called the vote a "blow to Mexican democracy" and a "coup d'état against the people of Mexico City".