Roman Abramovich - the owner of Chelsea Football Club - must be among those to face UK sanctions over Ukraine, Sir Keir Starmer has said.
The Labour leader accused Boris Johnson of being slow to target individuals who "prop up" Vladimir Putin's regime.
The PM said he could not comment on individual cases but UK sanctions were already "having an effect in Moscow".
Mr Abramovich has previously denied having close financial ties with Vladimir Putin or the Kremlin.
The BBC has contacted his spokesperson for a response to Sir Keir's claims.
The 55-year-old, who gave "stewardship and care" of Chelsea to its foundation trustees following Russia's invasion of Ukraine, is reported to be trying to sell the club.