An award-winning local journalist and Agence France-Presse contributor who reported on violent drug gangs in northwestern Mexico was shot dead in the street Monday, a judicial source told AFP.
Riodoce confirmed the news of Valdez's killing on its website.
Mexican president Enrique Peña Nieto said Monday afternoon that he has directed the federal police to help local authorities investigate "this outrageous crime".
The U.S. ambassador here, Roberta Jacobson, also sent out a Twitter message condemning the slaying of the journalist.
Eleven journalists were murdered and 426 attacks on the media were registered in Mexico in 2016, the press rights group Article 19 said.
Valdez's slaying came less than two weeks after a CPJ delegation met in Mexico City with Pena Nieto and other top government officials.
Last month, a newspaper in the border city of Juarez closed due to the climate of insecurity and impunity for killings of journalists.
Last weekend, seven journalists were briefly detained and threatened by a large group of armed men in the state of Guerrero.
He had written about the Sinaloa drug cartel and its now-detained founder Joaquin "El Chapo" Guzman. The former cartel chief was extradited to the United States in January on a range of charges.
Mexican and foreign journalists paid homage to Valdez on social media, describing him as a courageous writer and generous friend whose killers must be brought to justice to deter future slayings.
He is at least the sixth journalist murdered in Mexico since early March, an unusually high number even for one of the world's deadliest countries for media professionals.
According to reports, the journalist specialized in covering the drug trafficking was driving at 12 p.m. along the Vicente Riva Palacio street when a gunman stopped him, forced him to get out of his auto and shot him dead.
Valdez, a veteran reporter who specialized in covering drug trafficking and organized crime, was slain Monday, May 15 2017, in the northern Mexico state of Sinaloa, the latest in a wave of journalist killings in one of the world's most risky countries for media workers. "One must protect oneself from everything and everyone, and there do not seem to be options or salvation, and often there is no one to turn to". He founded RioDoce in 2003, which has won several awards.