Jorge Celestino Ruiz, who worked for the newspaper El Grafico de Xalapa, was killed on Friday night in the violence-plagued state of Veracruz, the mayor of the state's capital Paulino Dominguez told AFP.
Ruiz's house was shot at in October and bullets were also "fired at his vehicle to intimidate him," said a police source, who asked for anonymity, and did not give further details.
Ruiz had stopped putting his name to his articles to keep a low profile, the reporter's colleagues also said.
State interior secretary Hugo Gutierrez "strongly condemned" the killing on Twitter and said it was an attack on freedom of expression.
No odds big enough for K-P's women journalists
The shooting occurred less than 24 hours after the director of online news website La Verdad de Zihuatanejo, Edgar Alberto Nava, was gunned down in the southern state of Guerrero, according to the local prosecutors office.
And on Tuesday, the body of Rogelio Barragan - head of news website Guerrero Al Instante - was discovered in an abandoned car's trunk in the State of Morelos.
Reporters Without Borders said eight journalists had been killed in Mexico this year up until Thursday.
Since 2000, around 100 reporters have been killed in the country.
Violence linked to drug trafficking and political corruption is rampant, and most crimes go unpunished.
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