MEXICO CITY -- Media rights groups on Friday demanded that authorities investigate the deaths of three journalists in Mexico over the past week.

On Thursday, radio journalist Filadelfo Sanchez Sarmiento was shot dead by two attackers as he walked out of the La Favorita 103.3 FM station in Miahuatlan de Porfirio Diaz in Oaxaca state, officials said.

The U.S.-based Committee to Protect Journalists condemned the killing. It said that Sanchez Sarmiento hosted a news program and had written for local newspapers. He had received threatening phone calls.

Also Thursday, journalist Juan Mendoza Delgado died from being run over by a car. He ran a news website in the city of Medellin de Bravo and had disappeared the day before his death. Days earlier, Veracruz Gov. Javier Duarte had lashed out at the press, accusing some of having links to organized crime and telling them to "be well behaved."

In Guanajuato state, Gerardo Nieto Alvarez, director of the weekly Tabano, died on June 26 in the town of Comonfort after being stabbed in the neck while drinking in a bar.

"We call on the Oaxaca, Veracruz and Guanajuato authorities to ensure that impartial, independent and thorough investigations are carried out and that those responsible for these despicable crimes are arrested," Reporters Without Borders program director Lucie Morillon said.

"We are appalled by all these murders of journalists in Mexico," she said. "Three deaths in a week -- when will the violence stop?"

According to CPJ, more than 50 Mexican journalists have been killed or disappeared since 2007.