A prominent politician from Spain's governing People's party was shot and killed on Monday afternoon as she was crossing a footbridge over the Bernesga river in the northern Spanish city of León.

Isabel Carrasco, 59, who led the provincial government in León, was shot several times in broad daylight as she walked the short distance from her home to the local party headquarters, said Ramiro Ruiz Medrano, the central government's representative in the region.

Witnesses heard several shots just after 5pm. "We thought they were firecrackers," one man told El País. "At that time the area is full of people, kids playing and lots of people walking their dogs."

Police have arrested a woman, 55, and her daughter, 35, said Ruiz Medrano, adding that they are the wife and child of a police inspector from the nearby town of Astorga. A source at Spain's ministry of the interior dismissed suggestions that the killing was politically motivated, saying instead that the daughter had been recently let go from her job at the provincial government and "a personal grudge" may have played a role.

The killing came in the final weeks of campaigning before the European Parliament elections on 25 May. As news of Carrasco's death spread across the country, political rallies held moments of silence and cancelled their campaign acts for the rest of the day.

PP politician Esteban González Pons called the loss of Carrasco, who had led the party in the León province since 2004, "irreparable." The party, he said, was "disoriented".

Isbael Carrasco was a strong and courageous woman … We have few politicians in Spain with the courage of Isabel Carrasco."

The party, he added, would be suspending most of its campaign activities on Tuesday as well, but had yet to decide on whether they would participate in a candidates debate scheduled for Tuesday night.

The region has declared three days of mourning for Carrasco, a career civil servant who became head of the provincial government in León in 2007 and who the Diario de León noted was "the most powerful woman in León during the last decade."

Residents and local politicians gathered at the crime scene to pay their respects, many of them expressing shock at a level of violence not seen since the Basque separatist group Eta declared an end to its armed activity in 2011, turning the page on nearly four decades of high-profile assassinations.

Prime Minister Mariano Rajoy, who reportedly was traveling to León on Monday night, released a statement slamming what he called a "vile" act. "Along with my most firm condemnation, I want to highlight that the forces and security bodies of the state, as well as the implicated administrations, have been working since the first moments to clarify the circumstances of this miserable crime and bring its author or authors to justice."

He added, "In these hours of anguish for those who knew and loved Isabel Carrasco, I would like, on behalf of myself and the government of Spain, offer our solidarity to her family and loved ones, as well as share our repulsion at the violent homicide that ended her life."