LONDON -- A lawyer says a Russian businessman who has associated with a prominent critic of Russian President Vladimir Putin has died in London. Andrei Borovkov told Russian media outlets on Tuesday that his client, Nikolai Gushkov, has died, but said he was unaware of the time and circumstances.

Reports in British and Russian media say Glushkov, who was in his late 60s, was found dead at his home in southwest London.

London's Metropolitan Police force says officers are investigating the "unexplained" death of a man found at a house in the New Malden area late Monday. It did not identify him by name.

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Glushkov was a friend of Boris Berezovsky, a Russian oligarch who died in London in 2013. An inquest failed to determine whether he had killed himself or died from foul play.

London police say counterterrorism detectives are leading the investigation "as a precaution because of associations that the man is believed to have had."

Police say there is no evidence to suggest a link to the March 4 poisoning of former spy Sergei Skripal and his daughter.

In 2013, Glushkov told the U.K.'s Guardian newspaper that he was skeptical that Berezovsky's death was a suicide.

"I'm definite Boris was killed," he said. "I have quite different information from what is being published in the media."