Ukrainian authorities have come under fire for the faked death of Russian journalist Arkady Babchenko, who was announced shot dead in a contract-style killing, only to reappear at a news conference the following day.

Press freedom groups have raised fears about the impact the stunt could have on journalists' work around the world and Stoltenberg added his voice to the chorus of concern.

"I would like to underline that I regret that this incident may undermine trust in the free press and be used to fuel propaganda," he told reporters.

"I strongly believe that the best way to make sure we are not victims of fake news is that we have a free and independent press."

There have been warnings that the Babchenko incident would lead to more accusations of "fake news" at a time when the distinction between credible and non-credible sources is becoming ever more crucial.

Babchenko and the Ukrainian authorities have defended staging the killing, saying it was done to foil a genuine assassination plot.

The Kremlin has said the affair is "at the very least bizarre" and dismissed accusations that it had attempted to kill Babchenko, who has been deeply critical of President Vladimir Putin's government.