The death of Bertha Gisela Gaytán has renewed concerns over violence in the lead-up to the nationwide election on June 2.

The shooting was the latest in a string of violence against political hopefuls ahead of Mexico’s June 2 general elections.

“These events are very regrettable because these are people are fighting to defend democracy,” López Obrador said during his daily news conference on Tuesday. “They’re out on the street, face to face.”

López Obrador’s remarks came in response to the death of Bertha Gisela Gaytán, a candidate representing the left-wing party he founded, Morena. She was running to be mayor of Celaya, northwest of Mexico City.

On Monday, the first day of her campaign, Gaytán rallied with supporters in the streets of San Miguel Octopan, a town just outside of Celaya.

A short social media video from the shooting shows a cluster of people chanting and waving maroon flags in support of Morena, when suddenly gunshots ring out. A scream is heard in the distance.

Multiple people were struck, including the city council candidate Adrián Guerrero. Several media reports on Tuesday indicated he later died at a nearby hospital.

The Associated Press news agency estimates that at least 15 political candidates have been killed since January as the general election approaches.

Observers say threats largely stem from organised crime and drug cartels that exercise sway over the Mexican political system through threats, bribery and corruption.

Police, however, have yet to identify suspects in the shooting and arrests have yet to be made. In the aftermath, the governor of Guanajuato, the state where the shooting occurred, pledged to seek justice for the killings.

“The cowardly attack that took the life of candidate Bertha Gisela Gaytán in Celaya will not go unpunished,” Governor Diego Rodríguez Vallejo wrote.

“With all firmness, I condemn this inhumane act and reiterate my full commitment that the state may coordinate with efforts at all levels of government in the electoral process and thereby assure the participants have the necessary protection.”

On the day of her death, Gaytán held a news conference indicating that she had requested security for her campaign.

“Assistance has already been requested through the state legal system in the party,” she said, according to Mexican media reports. “The citizens are on our side, but of course, we are going to have security protocols.”

The city of Celaya has one of the highest homicide rates in the world, with an estimated 109.4 murders per 100,000 inhabitants.

But even elsewhere, violence has struck political campaigns in the run-up to the election.

For example, in February, two mayoral candidates were shot in Maravatío, in the west-central state of Michoacán.

One hailed from the right-leaning National Action Party and the other was from the Morena Party.

The last time Mexico held a nationwide election – in 2021, when state, local and national legislative seats were up for grabs – an estimated three dozen political candidates were killed.

Mexico is currently in the midst of another high-profile election, this time with the presidency hanging in the balance.

Presidents are limited to a single six-year term, meaning López Obrador is unable to run. But his protégée, former Mexico City Mayor Claudia Sheinbaum, is leading the race, with a strong lead over Senator Xóchitl Gálvez.