Reporters Without Borders (RSF) on Monday urged Brazil to take "concrete and effective" measures to protect journalists after two reporters were murdered in May.

In an open letter to President Dilma Rousseff, the NGO condemned the "brutal" killings, noting that Brazil ranks third globally behind Mexico and Honduras for murders of reporters on assignment.

The organization said a total of 38 journalists were assassinated in Brazil between 2000 and the end of last year as they investigated crimes including corruption and human rights abuses.

May saw two killings of journalists investigating reports of drug trafficking and child prostitution.

One was found decapitated.

RSF called on Rousseff to "end the prevailing impunity for crimes of violence against media personnel in her country," while decrying a growing trend of violence which claimed the lives of at least 15 journalists in the past three years.

"The impunity prevailing in most of the cases increases the probability of their recurring," the RSF asserted.

The RSF noted that the Brazilian Association of Investigative Journalists (ABRAJI) had logged 38 cases of abusive treatment of reporters during last year's World Cup alone, primarily blamed on heavy-handed military police.

"Combatting impunity must be a priority. Journalists will continue to be in danger as long as crimes of violence against them are not the subject of independent, impartial and thorough investigations that result in those responsible being identified and punished," RSF concluded.