MEXICO CITY — Three people, including a minor, were being held by the authorities on Sunday in the killing of the newly inaugurated mayor in Temixco, a central Mexican city.

Gov. Graco Ramírez of the state of Morelos, which contains Temixco, blamed organized crime for killing the mayor, Gisela Mota, 33, a former federal lawmaker who had been sworn in as mayor less than a day before she was shot in her home on Saturday morning.

Mr. Ramírez ordered more security measures for all of the state’s mayors, though he gave no details on what that involved.

Ms. Mota’s center-left Democratic Revolution Party released a statement describing her as “a strong and brave woman who, on taking office as mayor, declared that her fight against crime would be frontal and direct.” Bishop Ramón Castro Castro of the nearby city of Cuernavaca celebrated Mass at Ms. Mota’s home on Sunday and later spoke critically of a state where some areas are in control of organized crime.