Russia’s most wanted Islamist rebel Doku Umarov, whom the authorities hoped to have killed in an air strike last month, is alive and well and preparing reprisals, according to an audio tape.

A man purporting to be Mr Umarov telephoned the North Caucasus service of Radio Free Europe (RFE/RL), saying that he was “absolutely healthy” in a message in the Chechen language, the radio said on its website late on Thursday.

It was not possible to verify the authenticity of the message although the radio said that its correspondents said the voice was “recognisably” that of Mr Umarov.

Russia has said some 17 Islamist rebels were killed in the air strike on March 29 in the Ingushetia region of Russia’s North Caucasus and security sources expressed hope at the time that Mr Umarov was among the dead.

But Mr Umarov’s death was never confirmed officially, with the authorities saying weeks of DNA analysis will be needed.

“There was an operation in which several mujahedin died,” the voice added.

“My death was announced too. They won’t receive any respite from me. I’m preparing my answer to them. They should expect news from me soon.”