Russian opposition leader Alexei Navalny duped a Russian FSB state agent into revealing details of an attack on him with the nerve agent Novichok, the investigative group Bellingcat reports.
Mr Navalny reportedly impersonated a security official to call the agent.
The agent, Konstantin Kudryavtsev, told him the Novichok had been placed in a pair of Mr Navalny's underpants.
Mr Navalny, who is still recovering in Berlin, posted a recording of the long conversation on his YouTube channel.
He collapsed on board a Russian airliner in August in the attack, which nearly proved fatal.
As part of Mr Navalny's ruse to elicit more details of the assassination attempt, Bellingcat says the call to Mr Kudryavtsev was set up to indicate it was coming from a Federal Security Service (FSB) landline.
In the conversation, Mr Navalny posed as a senior official seeking details for a report on the FSB operation.
Mr Kudryavtsev told him the swift response of the airline pilot and the emergency medical team in Omsk, Siberia - where Mr Navalny was first treated - could have been the reason for the failure to kill him.
Mr Kudryavtsev said he had been sent to Omsk later to seize Mr Navalny's clothes and remove all traces of Novichok from them.
The BBC's Steven Rosenberg, in Moscow, says publication of the recording will be a huge embarrassment for the Kremlin, which continues to deny any link between the Russian state and poisoning of President Putin's most vocal critic.
Last week Mr Putin told a huge TV audience that the Bellingcat investigation - carried out with other Western media partners - was a "trick" invented by US intelligence.
But he added that it was right for the FSB to be shadowing Mr Navalny.
The Bellingcat report last week named several FSB agents - chemical weapons specialists - who, it alleged, had been tailing him for years before the attempt on his life.
Mr Navalny has millions of followers on social media, where he denounces Mr Putin's United Russia party as deeply corrupt and full of "crooks and thieves". He says Mr Putin runs a "feudal" system of patronage "sucking the blood out of Russia".
In the summer, before the August poisoning, Mr Navalny campaigned to get several of his supporters elected to councils in Siberia.