A journalist was killed on Friday in northern Mexico, authorities said -- the sixth such murder this year in one of the world's most dangerous countries for reporters.

The Latin American nation is on course for one of its deadliest years yet for the press, prompting calls from rights groups for authorities to end a culture of impunity.

"I condemn the act in which Juan Carlos Muniz, a worker at the Testigo Minero (Mining Witness) news portal, was deprived of his life," tweeted the governor of the northern state of Zacatecas, David Monreal.

He said that prosecutors had been instructed to find the perpetrators of the killing in Fresnillo, a city located in an area known for its silver mining and, in recent years, cartel-related violence.

"Neither this, nor any other crime, can go unpunished," Monreal added.

Zacatecas is one of the Mexican states hardest hit by drug violence, due to a turf war between the Sinaloa and Jalisco New Generation cartels for control of lucrative drug smuggling routes to the United States.

Testigo Minero condemned the killing of its journalist and demanded that the authorities identify those responsible.

"The cowardly murder of our colleague and friend has shocked a large part of the society of Fresnillo and the state, as well as the journalistic profession," the media outlet said.

The Zacatecas prosecutor's office said it had opened an investigation into the killing.

Around 150 journalists have been murdered in Mexico since 2000, and only a fraction of the crimes have resulted in convictions, according to media watchdog Reporters Without Borders (RSF).

Last month US Secretary of State Antony Blinken voiced concern about the string of killings, calling for "greater accountability and protections for Mexican journalists."

President Andres Manuel Lopez Obrador described the top US diplomat's remarks as "interfering" and said that he appeared to have been "misinformed."

The country of 126 million people, plagued by drug cartel-related violence, ranks 143rd out of 180 nations in RSF's World Press Freedom Index.

Given the poor pay, media workers in Mexico often combine journalism with other jobs, as was the case with Muniz who also worked as a taxi driver, according to Testigo Minero.

More than 340,000 people have been murdered across Mexico since the government deployed the military in the war on drugs in 2006, according to official figures.