Mexican drug trade reporter, Javier Valdez has been shot dead

Mexican journalist Javier Valdez, known for his award-winning coverage of the drug trade, has been shot dead.

Unidentified attackers opened fire on him on Monday in Culiacan city in the north-western state of Sinaloa, where he lived and worked. Valdez, 50, received the International Press Freedom Award from the Committee to Protect Journalists (CPJ) in 2011 for his work.

He is one of several journalists who have been killed in Mexico this year.

Valdez was shot dead on the street near the premises of the Mexican news weekly he had founded, Ríodoce.

During his career spanning nearly three decades, Valdez wrote extensively on drug-trafficking and organised crime in Mexico, including the powerful Sinaloa drug cartel.

The cartel is believed to be responsible for an estimated 25% of all illegal drugs that enter the US via Mexico.

Its founder Joaquin Guzman, also known as "El Chapo" (Shorty), was captured in 2014 and is currently in jail awaiting trial in the US.

Mexico's President Enrique Peña Nieto condemned the killing, calling it an "outrageous crime", and added that his government remained committed to press freedom.

Sinaloa state attorney general Juan Jose Rios said they were investigating the death, and would protect Valdez's family and colleagues."Above all else we are interested in Javier's family," he told reporters.

The CPJ's Mexico representative Jan-Albert Hootsen said Valdez's killing was "an attack on journalism, all journalists throughout Mexico".

Valdez and his publication had been threatened before. He told the freedom of expression organisation Index on Censorship last month that a hand grenade had been thrown into Ríodoce's offices in 2009, "although it only caused material damages".

"I've had phone calls telling me to stop investigating certain murders or drug bosses. I've had to suppress important information because they could have my family killed if i mention it." Sources of mine have been killed or disappeared.

The government couldn't care less. They do nothing to protect you.

There have been many cases and this keeps happening." Speaking at a launch of his book last year, he said being a journalist "is like being on a blacklist" and that gangs "will decide what day they are going to kill you".

In March, after journalist Miroslava Breach was shot dead, Valdez was quoted as saying "No to silence" and "Let them kill us all". Like Valdez, Breach had reported on organised crime, drug-trafficking and corruption.

Other Mexican journalists killed this year include freelancers Maximino Rodríguez and Cecilio Pineda Birto, according to the CPJ.

The CPJ says at least 40 journalists have been killed in Mexico since 1992.