More than 30 journalists have been killed worldwide in the last two years and countless more are at risk, according to Reporters Without Borders.
Italian mafia in particular are believed to target journalists looking into their activity, in Italy and beyond.
Both Daphne Caruana Galizia, killed last year by a car bomb in Malta, and Jan Kuciak, shot with his girlfriend in Slovakia in February, had been investigating the Italian mafia and its links with local politicians.
196 Italian journalists had some kind of police protection in 2017, with a dozen living under permanent police guard, including Roberto Saviano, the author of the bestselling book "Gomorra" about the Naples crime syndicate, the Camorra.
Gomorrah author Roberto Saviano. Photo: Christophe Simon/AFP
"The Mob has spread its tentacles around the globe faster than all the multinationals combined," Reporters Without Borders (RSF) said in a new report on the dangers.
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"From Beijing to Moscow, from Tijuana to Bogota, from Malta to Slovakia, investigative journalists who shed light on the deals that involve organised crime unleash the wrath of gangsters, whose common feature is an aversion to any publicity unless they control it," said its author, French investigative journalist Frederic Ploquin.
He said the only way to counter the threat was for reporters to work together to protect each other.
The biggest danger was in investigating corruption, Ploquin said, now that ruthless crime groups have "established a kind of pact with the state" in many countries, "to the point that you cannot tell where one stops and the other begins."
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"How is it possible that Mexico's drug cartels sprout like mushrooms without the support of part of the state's apparatus?" asked RSF,
Nine of the 14 journalists murdered worldwide in 2017 by organised crime groups were killed there.
Eight more journalists have been killed so far in 2018.
Three reporters were also killed this year in Brazil and three more elsewhere in Latin America. And an Indian journalist who was investigating his country's "sand mafia" was run over by a truck.
Earlier this week, Italian mafia experts said that the 'Ndrangheta are now operating “on every continent, and are spreading.”