Of those, two in five subsequently experienced physical violence, it said in a report released on World Press Freedom Day. More than 900 reporters were questioned for the poll.

The UN Educational, Scientific and Cultural Organization warned of an increase in violence against and intimidation of journalists reporting on the environment and climate.

"Without reliable scientific information about the ongoing environmental crisis, we can never hope to overcome it," UNESCO director general Audrey Azoulay said in a statement.

"And yet the journalists we rely on to investigate this subject and ensure information is accessible face unacceptably high risks all over the world, and climate-related disinformation is running rampant on social media."

UNESCO said at least 749 journalists and news media outlets reporting on environmental issues were "targeted with murder, physical violence, detention and arrest, online harassment or legal attacks" between 2009 and 2023.

More than 300 of those attacks occurred between 2019 and 2023 -- a 42 percent increase on the preceding five-year period.

"The problem is global, with attacks taking place in 89 countries in all regions of the world," the agency added.

- 'Fear of being attacked' -

At least 44 environmental journalists have been killed for their work in the past 15 years, with convictions in only five cases, said the report.

On top of hundreds of reported physical attacks, "a third of journalists surveyed said they had been censored," it added.

"Almost half (45 percent) said they self-censored when covering the environment due to fear of being attacked, having their sources exposed, or due to an awareness that their stories conflicted with the interests of concerned stakeholders."

At a press freedom conference in Chile this week, UNESCO will announce the launch of a grants program to provide legal and technical support to over 500 environmental journalists facing persecution, said the statement.