Sen. Mark Warner, vice chairman of the Senate Intelligence Committee, says the attorney general's investigation of the origins of the Russia probe is endangering one of the US's major spy partnerships.

William Barr's efforts to question British and Australian officials "puts in jeopardy the whole Five Eyes relationship," Warner said.

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WASHINGTON (Reuters) - US spy agencies' critical partnerships with English-speaking counterparts could be undermined by Attorney General William Barr's investigation into the roots of a probe of Russian efforts to interfere in the 2016 election, a top Senate Democrat said.

Senate Intelligence Committee Vice Chairman Mark Warner told Reuters that Barr's recent efforts to question British and Australian officials about how and why their intelligence agencies started collecting information linking President Donald Trump's campaign to Russia amounted to "asking our most trusted partners to weigh in on political matters."

"This puts in jeopardy the whole Five Eyes relationship," Warner said, referring to a post-World War II arrangement under which spy agencies of the US and four English-speaking allies — Britain, Canada, Australia and New Zealand — share secrets and divide up the world into geographical zones of expertise.

"For the most part, Trump IC (intelligence community) appointees have done a pretty good job maintaining their integrity," Warner added. But he said he worries that "sometimes it feels like the administration doesn't ever get it."

He said agencies must "speak truth to power and not allow their services to be co-opted. We as a committee have to have their backs."

Attorney General William Barr in Washington, DC, October 3, 2019. Reuters

Warner was responding to reports that Barr and US Attorney John Durham of Connecticut had approached British, Australian and Italian authorities with questions about the bona fides of sources such as Josef Mifsud, a Maltese academic whose gossip about alleged Russian possession of Hillary Clinton emails helped to trigger the initial FBI investigation.

Justice Department officials did not immediately respond to a request for comment on Friday. Barr has told CBS News that official explanations for the FBI's investigation "don't hang together."

Some former law-enforcement officials have raised concerns Barr is using the Justice Department to chase unsubstantiated conspiracy theories that could benefit Trump politically. Special Counsel Robert Mueller's Russia investigation concluded Moscow interfered in the 2016 election to help Trump.

Following a visit to Britain in July for a summit of Five Eyes officials, Barr held a private meeting with British Attorney General Geoffrey Cox. The subject matter of the meeting has not been made public.

Stephan Roh, a Zurich lawyer who represented Mifsud, said he has not heard from the academic for some time. He said Mifsud was represented by a London law firm in connection with US investigations. A representative of the London law firm, Howard Kennedy, declined to comment.

(Reporting By Mark Hosenball; editing by Scott Malone and Nick Macfie)