Mexico City (CNN) -- A Mexican mayor campaigning for the president's sister in a gubernatorial race was fatally shot in the southeastern state of Michoacan, the state attorney general's office said.
The killing of La Piedad Mayor Ricardo Guzman Romero on Wednesday is the latest in a number of mayoral killings dating to last year. According to CNNMexico, 18 mayors have been killed in 2010 and 2011.
But Guzman's death garnered extra attention because he was killed in President Felipe Calderon's home state, and because he was campaigning for the president's sister, gubernatorial candidate Luisa Maria Calderon. She is running as a candidate for the National Action Party, or PAN, the same party to which the president belongs.
The attack came just 11 days before the state elections, where in addition to a governor, 40 lawmakers and 113 mayors will be chosen.
Guzman was elected mayor in 2008, and his term was to end in January.
"At the moment, the federal authorities and military are in charge (of the case)," Michoacan attorney general's office spokesman Armando Soto La Marina said.
According to authorities, Guzman was participating in a campaign event, walking down one of his town's boulevards, when a black vehicle approached and a gunman shot from inside.
The shooter escaped, and the mayor was taken to a hospital, where he died, authorities said.
Luisa Maria Calderon said she was saddened by the killing, but that "we're not going to stop our fight for Michoacan."
Michoacan has long been a center of drug cartel violence. It was where President Calderon initiated his campaign against the cartels in 2006.
Last year, the PAN and an allied party declined to run candidates in at least 20 mayoral races in Michoacan because of insecurity.