A Mexican journalist known for his coverage of the country's drug war was killed in the city of Culiacan, security officials said.
Javier Valdez, 50, was killed on Monday while walking near the offices of Riodoce, a newsweekly he co-founded, the officials told Efe news.
The shots were fired from a passing vehicle.
Recognised as an expert on the impact of the drug trade on Mexican society, Valdez was honoured in 2011 by the US-based Committee to Protect Journalists with the International Press Freedom Award.
Investigators will look into the possibility that Valdez's killing was connected to his work as a reporter, state Attorney General Juan Jose Rios Estavillo told the media.
The office of the federal Special Prosecutor for Offenses against Press Freedom will send a team to take part in the investigation, he said.
Authorities are also concerned to "safeguard" Valdez's family and other members of the Riodoce staff, the attorney general said, appealing to members of the journalists guild to come forward with any information that could aid the probe.
Valdez was the Sinaloa correspondent for national daily La Jornada and the author of several books.
Last weekend, seven journalists were briefly detained and threatened by a large group of armed men in the state of Guerrero.
Mexico is one of the most dangerous countries in the world for journalists to work in.
A total of 126 journalists have been killed in Mexico since 2000.
Eleven journalists were murdered and 426 attacks on the media were registered in Mexico in 2016, the press rights group Article 19 said.