MEXICO CITY – Gunmen assassinated the front-running candidate for governor of a Mexican border state Monday in what President Felipe Calderon called an attempt by drug gangs to sway local and state elections this weekend.

The assailants ambushed Rodolfo Torre’s vehicle as he headed to the airport in Ciudad Victoria, capital of Tamaulipas, a state torn by a turf battle between two rival drug cartels. At least four other people traveling with him were killed.

“Today has proven that organized crime is a permanent threat and that we should close ranks to confront it and avoid more actions like the cowardly assassination that today has shaken the country,” Calderon said. “We cannot and should not permit crime to impose its will or its perverse rules.”

Torre, of the Institutional Revolutionary Party, or PRI, is the first gubernatorial candidate killed in Mexico in years.