An overwhelming majority of killings of journalists across the world go unpunished, a United Nations agency reported on Wednesday.

"Impunity for killings of journalists remains unacceptably high at 86 percent," said UNESCO, the United Nations cultural organisation whose brief includes media issues.

UNESCO called for "all necessary measures to ensure that crimes committed against journalists are properly investigated and their perpetrators identified and convicted."

The organisation called the global immunity rate for journalist killings "shockingly high" in a report to coincide with the International Day to End Impunity for Crimes Against Journalists, a UN-backed initiative.

UNESCO Director-General Audrey Azoulay said in a statement that "freedom of expression cannot be protected when there is such a staggering number of unresolved cases".

She said impunity had a "chilling effect on investigative reporting".

While UNESCO welcomed a 9-percentage-point drop in the impunity rate over the past decade it said this was insufficient to stop what it called "the spiral of violence".

In 2020 and 2021, the period covered by the report, of the 117 journalists murdered for doing their job, 91 were killed while off the clock.

"Several were killed in front of family members, including their children," it said.

UNESCO said it was working with member states to develop and implement national media laws and policies.

It was also training judges, prosecutors and security forces "to enforce the rights of journalists and ensure that attacks against them are investigated and prosecuted".