A Russian tech entrepreneur on Monday began a defamation claim against the British author of a controversial report at the heart of 2016 US election meddling allegations first leaked to BuzzFeed.

Alexej Gubarev said in documents released in London's High Court that former UK intelligence officer Christopher Steele was responsible for the US news site's January 2017 publication of his dossier.

Some of its findings were used by special counsel Robert Mueller to conduct his own investigation that found evidence of Russian interference but no collusion with Donald Trump's team.

Both Gubarev and Steele attended the opening hearing but did not give evidence on Monday. Buzzfeed is not a defendant in the case.

The five-day hearing covers the tumultuous few months that followed Trump's November 2016 US presidential election victory.

Steele's firm Orbis collected raw intelligence alleging that Kremlin officials had gathered compromising material on Trump during the years when he was still a New York property tycoon.

His dossier alleged that Russian intelligence agencies hacked into Democratic Party servers to collect damaging material on opponent Hillary Clinton.

It accused Gubarev's tech company Webzilla of conducting "operations against the Democratic Party leadership".

The report was published by BuzzFeed in January 2017.

"The central question for the court on liability, and the one to which the majority of material before the court is directed, is whether the defendants were responsible in law for the publication of the Steele Dossier by BuzzFeed," Gubarev's lawyers said in a statement.

"The claimant's case is that the answer is demonstrably yes."

The claim said it expected the damages to be capped by the court at £325,000 ($410,000, 358,000 euros).

Steele and his company said they had nothing to do with Buzzfeed's "unauthorised online publication".

The defendants "did not intend the December memorandum or its content to be made public (and) did not provide the December memorandum to BuzzFeed or any other media organisation."

- 'Not a public figure' -
The court case is being held in London because Gubarev claims that he has friends and business connections in Britain that have been damaged by Steele.

Yet little is known about Gubarev and his Cyprus-registered firm.

A report by a former FBI cyber crime division official concluded last year that the internet servers provided by Gubarev's firm were used by Russian intelligence agencies to tap into the Democratic Party servers.

Gubarev's court filings did not refute this but denied "knowing involvement" in the suspected hack.

The court documents said Gubarev was born in Russia but has been a resident of Cyprus for 18 years.

It did not provide his age but said "his eldest daughter is pursuing higher education in the UK".

"He is by no means a public figure, but he is well known within the technology sector, and his Cypriot community," Gubarev's court papers said.

- John McCain aide -
Steele's filing explained that BuzzFeed obtained the report through the office of the late US senator John McCain.

Yet the circumstances under which this happened are in dispute.

McCain's aide David Kramer admitted in a US District Court filing unsealed in Miami last year that he showed the dossier to BuzzFeed reporter Ken Bensinger.

"Kramer testified that Bensinger took photos of the Dossier when Kramer was out of the room, even though he asked Bensinger not to," the 2019 filing says.

But it adds that in "a later declaration, Kramer stated that he had no objection to Bensinger taking a hard copy and had provided hard copies to other journalists".

Steele's court filing said he had only provided copies of his report to a "senior UK national security official" and Kramer to give to McCain.

"No other copies of the pre-election memoranda (were) provided with Mr Steele's knowledge or consent" it said.

Steele added that he felt "deep dismay and disappointment... at learning that Mr Kramer had seriously betrayed his trust".

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