British police say they have no evidence to suggest third-party involvement in the unexplained death of Boris Berezovsky, the self-exiled Russian tycoon whose body was found at a property outside London.

Police say an employee of Berezovsky said he had called an ambulance on Saturday after becoming concerned for the former oligarch's welfare.

They added that the employee told police he forced open a bathroom door which had been locked on the inside and discovered Berezovsky's body on the floor.

Berezovsky was pronounced dead by a paramedic.

Police said Sunday it would be wrong to speculate on the cause of death until an autopsy is completed.

Earlier Sunday, police said chemical and radiation experts found no hazardous materials in their search of the property in Ascot, a town 40 kilometres west of London. Berezovsky was 67, and Thames Valley police say his death is being treated as "unexplained."

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A British police officer stands guard at a cordon off road leading to the residence of Boris Berezovsky, March 24, 2013. Sang Tan/Associated Press

Police said officers specially trained in chemical, biological, radiological and nuclear materials have given the scene the "all clear."

"Officers found nothing of concern in the property and we are now progressing the investigation as normal," a statement from police said, adding that the majority of the cordon put in place around the property has now been lifted.

Berezovsky — who had survived a number of assassination attempts — amassed a fortune through oil and automobiles during Russia's chaotic privatization of state assets following the collapse of the Soviet Union in the early 1990s.

Once a member of Russian President Boris Yeltsin's inner circle, Berezovsky fell out with Yeltsin's successor, Putin, and moved to Britain in the early 2000s to escape fraud charges that he said were politically motivated.

He became a strident and frequent critic of Putin, accusing the leader of ushering in a dictatorship, and accused the security services of organizing the 1999 apartment house bombings in Moscow and two other Russian cities that became a pretext for Russian troops to sweep into Chechnya for the second war there in half a decade.

Berezovsky 'spared no expense' to fight Putin

Putin's spokesman acknowledged Sunday that the Russian president considered Berezovsky an enemy with clearly stated intentions to fight.

"We know for certain that he spared no expense in support of processes, within Russia and beyond, that could be said to have been directed against Russia and Putin," spokesman Dmitry Peskov said on the independent cable television channel Rain. "He definitely was Putin's opponent, and unfortunately not only his political opponent, but most likely in other dimensions as well."

In recent years, Berezovsky fended off legal attacks that often bore political undertones — and others that bit into his fortune.

Russia repeatedly sought to extradite Berezovksy on a wide variety of criminal charges, and the tycoon vehemently rejected allegations over the years that he was linked to several deaths, including that of slain journalist Anna Politkovskaya and ex-KGB agent Alexander Litvinenko.

Berezovsky won a libel case in 2010 against a Kremlin-owned broadcaster that aired a show in which it was suggested he was behind the poisoning of Litvinenko, who had fled Russia with Berezovsky's help after accusing officials there of plotting to assassinate political opponents.

He took a hit with his divorce from Galina Besharova in 2010, paying what was at the time Britain's largest divorce settlement. The figure beat a previous record of 48 million pounds ($73.1 million) and was estimated as high as 100 million pounds, though the exact figure was never confirmed.

Legal battle with former business partner

Last year, Berezovsky lost a High Court case against fellow Russian Roman Abramovich and was ordered to pay 35 million pounds ($53.3 million) in legal costs.

Berezovsky had claimed that Abramovich, the billionaire owner of Chelsea Football Club, cheated him out of his stakes in the oil group Sibneft, arguing that he blackmailed him into selling the stakes vastly beneath their true worth after he lost Putin's good graces.

But a judge threw out the case in August, ruling that Berezovsky was a dishonest and unreliable witness, and rejected Berezovsky's claims that he was threatened by Putin and Alexander Voloshin, a Putin ally, to coerce him to sell his Sibneft stake.

It also recently emerged that Berezovsky ran up legal bills totaling more than 250,000 pounds in just two months of a case against his former partner, Elena Gorbunova, with whom he had two children and who claimed the businessman owed her millions.

Earlier this week, The Times of London newspaper reported that Berezovsky was selling property — including an Andy Warhol portrait of the former Soviet Union leader Vladimir Lenin — to settle his debts and pay expenses owed to lawyers.

News of Berezovsky's death has prompted conspiracy theories along with speculation as to his state of mind, given his recent financial setbacks.

Ilya Zhegulev, a journalist with the Russian edition of Forbes magazine, said he spoke with Berezovsky the day before he died and discussed the tycoon's decision to flee Russia in 2000.

The journalist quoted Berezovsky as saying that during his years in London he had lost the meaning of life.

"I no longer want to be involved in politics," Zhegulev quoted Berezovsky as saying in a story published Saturday on the Forbes.ru website.

He said Berezovsky told him that he wanted nothing more than to return to Russia. The former oligarch said he had changed his views on Russia, saying he now understood that it should not look to Europe as a model.

"I had absolutely, idealistically imagined that it was possible to build a democratic Russia. And idealistically imagined what democracy was in the centre of Europe. I underestimated the inertia of Russia and greatly overestimated the West. This took place gradually. I changed my understanding of Russia's path," he quoted Berezovsky as having said.