An international news media advocacy group has urged Russia to conduct a thorough investigation in to the death of a journalist who died after falling from a fifth floor window in his apartment building.

Ivan Safronov (file photo)

The Vienna-based International Press Institute expressed in a statement Wednesday deep concern over the death of Russian journalist Ivan Safronov Friday.

Safronov's newspaper, Kommersant, said the military affairs writer was working on a report claiming Russia planned to sell sophisticated missiles to Syria and Iran.

The daily also said that Safronov was warned he would be charged with revealing state secrets if he reported that Moscow had signed a deal with Syria for the sale of MIG-29 jets.

Russian police suggested Monday that Safronov's fall was either an accident or a suicide, after preliminarily ruling out any criminal activity. But prosecutors also have opened an inquest.

The institute's director, Johann Fritz, also said that the deaths of many other Russian journalists and the impunity which accompanies these deaths cause great concern.

The Brussels-based International News Safety Institute released a report Tuesday, saying that the number of journalists killed in Russia is second only to that of Iraq.

Some information for this report was provided by AP.