Rodolfo Torre Cantu, who was running for governor in the north-eastern state of Tamaulipas, was shot along with four of his supporters.

Police say he was on his way to a series of campaign rallies when his convoy was ambushed by hooded gunmen.

He was standing for the Todos Tamaulipas coalition in Sunday’s gubernatorial elections.

Mr Torre Cantu of the Institutional Revolutionary Party, or PRI, was attacked near Ciudad Victoria, where he was going to catch a flight to Matamoros for an end-of-campaign event.

His rival for the post of Tamaulipas governor, Jose Julian Sacramento of the National Action Party, cancelled his campaign meetings in Matamoros following the killing.

Mr Sacramento said he had known Mr Torre Cantu for years and respected him.

Tamaulipas has been the scene of a fierce turf war between rival drug gangs fighting over access to lucrative drug smuggling routes to the United States.