Ukraine staged the murder of a Russian dissident journalist in Kiev on Tuesday in what it said was a sting operation to foil a Russian assassination plot.
Arkady Babchenko sent shock waves around the world when he arrived at a news conference on Wednesday, less than 24 hours after he was reported dead.
The head of Ukraine's security services, Vasyl Hrytsak, said the elaborate sting was set up to catch hitmen paid by Russian forces.
Police said they had made one arrest.
Babchenko's wife said on Tuesday that she had found her husband at the entrance to their apartment block with bullet wounds in his back, and he was reported to have died in an ambulance on the way to hospital.
That story was widely reported by media around the world, until Wednesday's sudden and extraordinary development.
There were gasps and applause at the press conference in Kiev as Babchenko entered the room. He thanked the Ukrainian security services for saving his life and said he had no choice but to take part in the sting.
"I did my job. I'm still alive," he said. "I have buried many friends and colleagues many times and I know the sickening feeling," he added. "I am sorry you had to experience it. But there was no other way."
Hours after the news broke, Babchenko tweeted to say he would "die at 96" after "dancing on Putin's grave", referring to the President of Russia, Vladimir Putin.
Babchenko fled Russia in 2017 after writing a Facebook post (in Russian) about a crashed Tu-154 transport plane, which went into the Black Sea while carrying a Red Army choir to Syria.
He claimed this Facebook post, in which he described Russia as an "aggressor", led to death threats and abuse from the Russian state.
What do we know about the operation?
Babchenko said he was informed a month ago about an alleged Russian plot to kill him. He said he agreed to cooperate with a counter-operation and was in constant contact with Ukrainian security services over the course of the past month.
He added that he thought security services had been planning the operation for up to two months.
Mr Hrytsak said the operation began after Ukrainian security services were informed about a Russian plot to kill the journalist.
He alleged that Russian security forces had recruited a Ukrainian citizen to find hitmen within Ukraine. He said the citizen approached several acquaintances, including war veterans, offering $30,000 (£22,600) for the contract killing, one of whom revealed the plot to the security services.