A mayor in the western Mexican state of Michoacan was shot and killed while distributing campaign material, authorities said.

Ricardo Guzman Romero, mayor of the municipality of La Piedad and member of the ruling conservative National Action Party, or PAN, was campaigning ahead of Michoacan elections on Nov. 13, when voters will select a governor, state lawmakers and 113 mayors.

Guzman was shot in the chest Wednesday and died later that day at a private hospital, the state Public Safety Secretariat told the media.

He was campaigning for the PAN's candidate to succeed him as mayor of La Piedad and the party's gubernatorial candidate in Michoacan, Luisa Maria Calderon, sister of President Felipe Calderon.

That state's Attorney General's Office, meanwhile, said Guzman and a group of young people were putting up a PAN banner at a commercial establishment when an SUV arrived carrying three or four gunmen, one of whom shot the mayor.

The attackers then fled in an unknown direction.

In remarks to the Televisa network, Luisa Maria Calderon lamented the death but vowed that her party would not be intimidated.

"Fear's not going to stop us," she said. "On the contrary, we want things to change" in Michoacan, a state that has been governed since 2002 by the left-wing Party of the Democratic Revolution, or PRD.

The president, who is participating in the G-20 summit in France, sent condolences to Guzman's family via Twitter and called him "the best mayor of La Piedad." He added that the politician was "killed in cowardly fashion. An honest man who wanted a better Michoacan."

A mountainous state with a Pacific coastline, Michoacan has been the scene of a turf war pitting the once-powerful La Familia Michoacana drug cartel against former allies Los Caballeros Templarios.

Speaking of Guzman, Luisa Maria Calderon referred to him as a "brave and generous warrior who was campaigning (for the PAN) on his day off and that's what we're all going to keep doing."

She recalled that Guzman had initially planned to run for the state legislature but changed his mind and decided to remain on as mayor after an attack on his police chief.

"If what the criminals want is for us to be afraid of them, we're not going to cooperate," the gubernatorial candidate said.

Guzman became the 20th mayor slain in Mexico since 2010 and the 28th murdered in the past five years, according to the National Federation of Municipalities of Mexico, which comprises 1,500 of the country's 2,500 mayors.

Drug-war violence has claimed nearly 50,000 lives across Mexico since December 2006, when Calderon took office and militarized the struggle against the cartels.