Counter-terror police are leading an investigation into the “unexplained” death of a man in London.
He is believed to be Russian businessman Nikolai Glushkov, who claimed political asylum in the UK after being convicted of fraud.
The Metropolitan Police said its specialist unit was looking into it “as a precaution because of associations that the man is believed to have had”.
There was no evidence linking the death to the incidents in Salisbury, it said.
In a statement, it said the man in his 60s had been found at a residential address in New Malden on Monday night.
The man has been identified, but not formally. However, next of kin have been informed.
UK political asylum
Mr Glushkov, 69, is the former deputy director of Russian state airline Aeroflot.
He was jailed in 1999 for five years after being charged with money laundering and fraud.
After being given a suspended sentence for another count of fraud in 2006, he fled to the UK to seek political asylum and became a critic of Russian President Vladimir Putin.
Mr Glushkov also had a close friendship with fellow Russian businessman Boris Berezovsky, who came to the UK in 1999 after falling out with Mr Putin.
Mr Berezovsky was found hanged in the bathroom of his Berkshire home in 2013 and an inquest recorded an open verdict.
By BBC security correspondent Gordon Corera
There may be nothing suspicious about the death of Nikolai Glushkov, but given the current context it is impossible for the police to do anything other than take it seriously and ask Counter Terrorism Command to lead the investigation.
In the past, there has been criticism of the police not taking such deaths seriously enough.
The Home Secretary has also today asked the police and MI5 to review a series of other deaths of Russians and Russian-linked individuals in the UK over the last decade or so.
One of those may well be Boris Berezovsky, who was found dead in 2013 and who was a close ally of Glushkov.
This is all a sign that the prism through which those past deaths are seen has changed. That is because the notion of what Russia might be capable of doing has changed.
The top priority though, for MI5 and police, will not be looking back at previous cases but instead the ongoing investigation in Salisbury.