London: British police said on Friday they had launched a murder investigation following the death in London of a Russian associate of late tycoon Boris Berezovsky.

"A murder investigation has been launched following the results of a post mortem into the death of 68-year-old Russian businessman Nikolai Glushkov," London's Metropolitan Police said in a statement, adding the cause of death was compression to the neck.

The police statement said that at this stage there was nothing to suggest a link to the attempted murders of former Russian spy Sergei Skripal and his daughter on March 4 or that poison was involved.

Earlier on Friday, Russia's Investigative Committee said it had opened a criminal investigation into both the attempted murder of Yulia Skripal and what it said was the murder of Glushkov. It also said it was ready to cooperate with British authorities on the two cases.

British Foreign Secretary Boris Johnson said on Friday it was "overwhelmingly likely" that Russian President Vladimir Putin himself had made the decision to use a military-grade nerve toxin to strike down Sergei Skripal.