London (CNN) -- Investigators are searching the London area home where the body of former Russian oligarch Boris Berezovsky was found for possible chemical, radiological or biological evidence, police said in a statement released early Sunday. Circumstances surrounding the death of Berezovsky, one of the most politically influential of Russia's oligarchs until a bitter falling out with the Kremlin, were not immediately known, and authorities in the United Kingdom said it was being investigated. "His death is currently being treated as unexplained and a full inquiry is under way," Thames Valley Police said in a statement. Officers, including specialized investigators, are conducting a number of searches "as a precaution."
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NEW: Authorities search the home for possible biological or chemical evidence
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Boris Berezovsky, 67, was a fierce critic of Russian Vladimir Putin and called for his overthrow
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Once considered one of Russia's richest oligarchs, his wealth was on the decline
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He survived two attempts on his life, including a car bomb
In 2003, as @placeholder was seeking his return, Berezovsky was granted political asylum by British authorities after it was determined he was wanted on political grounds, not criminal, according to published reports at the time.
In 2003, as Russia was seeking his return, Berezovsky was granted political asylum by @placeholder authorities after it was determined he was wanted on political grounds, not criminal, according to published reports at the time.