MOSCOW: Russian opposition leader Alexei Navalny said Monday he had tricked a security agent into admitting the Federal Security Service (FSB) sought to kill him this summer and placed poison in his underwear.

In a blog post the Kremlin critic said he phoned a man named Konstantin Kudryavtsev, who he said was a chemical weapons expert with the FSB domestic intelligence agency.

"I called my killer. He confessed everything," Navalny said on Twitter.

Navalny said he disguised his phone number and presented himself as an aide to Security Council chief Nikolai Patrushev, explaining he needed information for an official report on the attempted poisoning.

The opposition leader published an audio recording and a transcript of the phone call and released a video of him conducting the conversation. He said that voice analysis "would demonstrate that it is indeed" Kudryavtsev speaking.

In the audio recording, the voice on the other end of the line initially sounds hesitant and cautious but eventually tells the story and explains why Navalny managed to survive the poison attack.

There were no immediate reactions from Russian authorities.

Navalny, 44, fell violently ill during a flight from Siberia to Moscow in August and was hospitalised in the Russian city of Omsk before being transported to Berlin by medical aircraft. Experts from several Western countries concluded that the Kremlin critic was poisoned with the Soviet-era Novichok nerve agent - a claim that Moscow has repeatedly denied.

A joint media report led by the Bellingcat investigative website last week revealed what it said were the names and photos of chemical weapons experts from the FSB that had tailed Navalny for years. In his blog post on Monday, the opposition leader said that last week he called the security agents identified in the report.