An ex-KGB chief suspected of helping the former MI6 spy Christopher Steele to compile his dossier on Donald Trump may have been murdered by the Kremlin and his death covered up, it's been claimed.

Oleg Erovinkin, a former general in the KGB and its successor the FSB, was found dead in the back of his car in Moscow on December 26 in mysterious circumstances.

Mr Erovinkin was a key aide to Igor Sechin, a former deputy prime minister and now head of Rosneft, the state-owned oil company, who is repeatedly named in the dossier.

He has been described as a key liaison between Mr Sechin and Russian President Vladimir Putin. Mr Steele wrote in an intelligence report dated July 19, 2016, he had a source close to Mr Sechin, who had disclosed alleged links between Mr Trump's supporters and Moscow.

The death of Mr Erovinkin has prompted speculation it is linked to Mr Steele's explosive dossier, which was made public earlier this month. Mr Trump has dismissed the dossier as "fake news" and no evidence has emerged to support its lurid claims.

The Russian state-run RIA Novosti news agency reported Mr Erovinkin's body was "found in a black Lexus . . . a large-scale investigation has been commenced in the area."

No cause of death has been confirmed and the FSB continues to investigate. Media reports suggested his death was a result of foul play. It was later claimed he died of a heart attack.

Christo Grozev, an expert on Russia-related security threats, believes Mr Erovinkin is the key source to whom Mr Steele refers in his dossier. Mr Grozev said on a blog: "Insiders have described Erovinkin to me alternately as 'Sechin's treasurer' and 'the go-between between Putin and Sechin'."

Mr Grozev, of Risk Management Lab, a think-tank in Bulgaria, said: "I have no doubt that at the time Erovinkin died, Mr Putin had Mr Steele's Trump dossier on his desk. He would - arguably - have known whether the alleged . . . story is based on fact or fiction.

"Whichever is true, he would have had a motive to seek - and find the mole. He would have had to conclude that Erovinkin was at least a person of interest."

Mr Steele (52) remains in hiding following his unmasking as the author of the Trump dossier.

Telegraph.co.uk