Imprisoned Russian opposition leader Alexei Navalny has told US President Joe Biden to go after Vladimir Putin's cash to rein him in instead of imposing sanctions on his cronies. 

'It's really simple. You want to influence Putin, then influence his personal wealth. It's right under your backside,' Navalny wrote to TIMEfrom prison where he is serving two and a half years in a penal colony for parole violations related to a fraud case he claims was politically motivated.