Isabel Carrasco, head of the provincial government in the northern Spanish city of Leon, was shot several times by a woman as she crossed a footbridge.
Spanish media report that a mother and daughter have been arrested, and that the daughter had recently been fired from the council.
Spain’s PM Mariano Rajoy has cancelled engagements.
Mariano Rajoy is head of the Popular Party (PP) to which Isabel Carrasco belonged.
Isabel Carrasco, 59, was the head of the PP in Leon as well as head of the local government.
The opposition Socialist Party and other parties also offered condolences and cancelled campaign events.
Isabel Carrasco was attacked on her way to a party meeting near her home at about 17:20 local time.
A police spokeswoman told AFP news agency: “We are investigating the participation of both [women] in the act.”
A spokeswoman for the Spanish interior ministry said: “Everything points to it being a personal act of vengeance unrelated to her public position.”
About 200 people gathered near the scene of her death, including the Mayor of Leon, Emilio Gutierrez, and several councilors and other local dignitaries, reported the ABC news website.
Witnesses told Spanish media that a woman shot at Isabel Carrasco as she crossed a bridge over the River Bernesga.
Two witnesses told Spanish newspaper El Pais they heard five shots.
“We thought they were firecrackers,” one of them said.
In a statement, the PP said campaign events for Monday and Tuesday had been cancelled, and thanked those who had offered condolences.
[youtube k5gUe0Botuw 650]