He said he was in fact alive and well.

"I would like to apologise for what you have all had to go through," Babchenko, who looked on the verge of tears at times, told reporters.

"I'm sorry, but there was no other way of doing it. Separately, I want to apologise to my wife for the hell that she has been through."

He went on to thank the Ukrainian Security Service, the SBU, for saving his life and said the most important thing was that what he called other big acts of terror had been thwarted. He did not specify what those planned acts were.

The SBU said Russia had sought to pay $US40,000 to assassinate Babchenko. SBU head Vasyl Hrytsak told the news conference that those behind the real assassination plot had been apprehended.

The murder "was ordered by Russia's security forces," he said Wednesday.

"The organiser was talking about killing another 30 people in Ukraine. We know some names but I won't name them."

The SBU said it had received information about the plot and had managed to prevent it.

Babchenko, a Putin critic, lived in the Ukrainian capital after receiving threats at home for saying he did not mourn the victims of a Russian military plane crash.

Ukrainian Prime Minister Volodymyr Groysman said in a social media posting late on Tuesday that he was convinced what he called "the Russian totalitarian machine" had not forgiven Babchenko for what Groysman called his honesty.

The Kremlin described such allegations as part of an anti-Russian smear campaign.

"This is the height of cynicism against the backdrop of such a brutal murder. It is anti-Russian bluster instead of talking about the need to conduct a thorough, objective investigation," Kremlin spokesman Dmitry Peskov told reporters before it was revealed that Babchenko was alive and well.

After Babchenko re-emerged on Wednesday, the Russian Foreign ministry said Ukraine has used is 'death' as propaganda.

Ukraine's shock ploy will further sour ties between Ukraine and Russia, post-Soviet allies who fell out following the ouster of Ukraine's pro-Kremlin leader in 2014. That prompted Putin to annex Crimea and back a war on the two nations' border.

The incident has echoes of this year's nerve-agent attack on a Russian double agent and his daughter in the UK, which triggered diplomatic expulsions around the world.

Babchenko rose to fame as a war correspondent in Russia. He travelled to the conflict in Ukraine and criticised the 2014 downing of Malaysia Airlines passenger flight MH17, which killed 298 people. Investigators from Australia and the Netherlands last week blamed Russia for the tragedy.

The journalist also sparked a backlash in Russia for his comments in a 2016 Facebook post on a Russian military plane crash. He said his comments had resulted in thousands of threats, his home address being published online and calls for him to be deported.

The plane, carrying 92 people, including dozens of Red Army Choir singers, dancers and orchestra members, crashed into the Black Sea on its way to Syria in December 2016, killing everyone on board.

Reuters, Bloomberg