Mexican authorities have not said whether they see the slayings as targeted. They come after a year of heightened political violence.

The private secretary and an adviser to the mayor of Mexico City were shot dead by gunmen on a motorcycle in an attack in the Mexican capital Tuesday.

By Diego Oré and Aida Pelaez-Fernandez MEXICO CITY (Reuters) -Two top aides of Mexico City Mayor Clara Brugada were shot dead after being ambushed by gunmen on a motorbike in a daytime attack in the city center on Tuesday.